Show Summary Details

Page of

PRINTED FROM OXFORD HANDBOOKS ONLINE (www.oxfordhandbooks.com). © Oxford University Press, 2018. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Handbooks Online for personal use (for details see Privacy Policy and Legal Notice).

date: 22 November 2018

The Postauricular Reflex as a Measure of Attention and Positive Emotion

Abstract and Keywords

The postauricular reflex is a muscular reaction that occurs behind the ear in response to short, abrupt sounds. Its magnitude increases with louder eliciting sounds, rotating the eyes in the direction of the eliciting sound, and flexing the head forward. The reflex exhibits prepulse inhibition, especially during attention to complex foreground stimuli. Its magnitude is larger (or potentiated) during pleasant than during neutral pictures, sounds, and videos that are highly arousing. This pattern is particularly evident for erotic, food, and nurturant scenes, suggesting it assesses more than just appetitive processing. This reflex’s potentiation varies across development; positively correlates with personality traits associated with well-being; and negatively correlates with such psychopathologies as depression, schizophrenia, and opioid dependence. It appears distinct from and uncorrelated with the startle blink reflex. New data suggest that activity in left frontal areas generates postauricular reflex potentiation during pleasant versus neutral pictures.

Keywords: postauricular reflex, positive emotion, appetitive processing, development, psychopathology, personality, attention, prepulse inhibition, left frontal, startle reflex

Introduction

The postauricular reflex is a reflex that occurs behind the ear in response to punctate (that is, short and abrupt) sounds. It pulls the ear upward and back (Bérzin & Fortinguerra, 1993). Kiang, Crist, French, & Edwards (1963) first isolated this reflex as an electrical potential over the postauricular muscle that is evoked by noise clicks in awake humans. Though this reflex is vestigial in humans—that is, it does not create visible motion in the pinna—it still provides information about multiple psychological processes. After considering basic influences on the measurement of the postauricular reflex, this article describes how this reflex has been used in psychology to assess attentional processes. It then details how this reflex has enjoyed a resurgence as a measure of positive emotion. Finally, possible mechanisms underpinning postauricular reflex modulation are sketched, followed by future research directions involving this reflex.

Measurement

Anatomy and neural circuitry.

The postauricular muscle typically lies midway up the ear and is present in 95% of people (Guerra et al., 2004). However, this activity is not visible in humans; rather, it reflects a vestigial reflex that orients the pinna in prosimians, whose ear musculature is better developed and whose evolutionary line diverged from hominids 22 million years ago (Hackley, 2015). Nevertheless, with the exception of the orangutan (genus Pongo), the postauricular muscle is present in all primates (Diogo & Wood, 2011) and can be traced phylogenetically through a large number of mammals (Diogo, Abdala, Lonergan, & Wood, 2008). The postauricular reflex has been described as an analog of Preyer’s reflex, a hybrid orienting and startle response to alerting sounds with a 6 millisecond (ms) onset latency that is frequently studied in guinea pigs (Davis, Lowell, & Goldstein, 1965).

Subsequent work clarified that the postauricular reflex—which may oscillate maximally in a 25–50 Hertz (Hz) frequency band (Mishra, Martinez, Sejnowski, & Hillyard, 2007)—is a myogenic (or generated from muscular activity) reflex instead of a cortical potential, though signal averaging is typically needed to reveal it (Cody, Bickford, & Klass, 1969; cf. Sandt, Sloan, & Johnson, 2009). Postauricular reflex magnitude recorded with surface electromyogram (EMG) electrodes is proportional to the number of postauricular muscle motor units activated as measured by transdermal recordings (De Grandis & Santoni, 1980). Administering curare (a reversible nicotinic acetylcholine inhibitor that temporarily paralyzes muscles) also abolishes the postauricular reflex (Jacobson, Cody, Lambert, & Bickford, 1964). Whereas other myogenic potentials (including the inion response, which occurs at the back of the head and measures vestibular processing) can be elicited with ulnar or photic stimulation (Bickford, Jacobson, & Cody, 1964; Cody & Bickford, 1969), the postauricular reflex can only be elicited with acoustic probes (Hackley, Ren, Underwood, & Valle-Inclán, 2017).

Furthermore, in contrast to the vestibular origin of the inion response (Cody, Jacobson, Walker, & Bickford, 1964), the postauricular reflex originates from afferent sensory input in the cochlea (Yoshie & Okudaira, 1969). From there, the cochlea sends input to the cochlear nucleus, which spreads activity bilaterally across both facial nerve nuclei, even with monaural stimulation (Douek, Gibson, & Humphries, 1973; Yoshie & Okudaira, 1969). The facial nerve represents the efferent pathway to the postauricular muscle that generates the postauricular reflex. The reflex is abolished on the side in which intracranial facial nerve palsies of various etiologies occur but not in patients with extracranial facial nerve palsies (Bochenek & Bochenek, 1976). Additionally, postauricular muscle activity can be used as an indicator of facial nerve conduction velocities (De Meirsman, Claes, & Geerdens, 1980), and postauricular reflexes are among the first EMG responses to recover from Bell’s palsy, which affects the facial nerve (Serra, Tugnoli, Cristofori, Eleopra, & De Grandis, 1986). This reflex arc creates more rapid responses than are typically seen in the startle circuit, which often has an onset latency between 45 and 50 ms (Hackley, Woldorff, & Hillyard, 1987) and includes the nucleus reticularis pontis caudalis (nRPC; Davis, Gendelman, Tischler, & Gendelman, 1982; Lee, López, Meloni, & Davis, 1996). The nRPC represents the juncture into which the amygdala provides input to make the startle reflex larger (or potentiated) during threatening versus neutral states (Hitchcock & Davis, 1986).

Placements, eye motion, and noise intensity.

Postauricular reflexes are largest when recorded using one electrode placed over the midpoint of the muscle and another placed along the back of the pinna nearest the crease between pinna and scalp (O’Beirne & Patuzzi, 1999). Initial reports indicated that turning the head toward the source of the eliciting sound could increase postauricular reflex magnitude (Davis, Engebretson, Lowell, Satterfield, & Yoshie, 1964). Subsequent work demonstrated that rotating the eyes toward the eliciting sound (Patuzzi & O’Beirne, 1999)—not the rotation of the head per se (Cook & Patuzzi, 2014)—enhances both postauricular muscle baseline activity and reflex magnitude. This pattern is consistent with Wilson’s oculoauricular phenomenon, in which moving the eyes to one side also moves the pinna on that side (Patuzzi & O’Beirne, 1999) that may result from the medial facial nucleus’s shared enervation of auricular and orbitoauricular muscles (Morecraft, Stilwell-Morecraft, & Rossing, 2004). Tucking the chin toward the neck (Patuzzi & O’Beirne, 1999) or other means of flexing the neck muscles forward (Hackley et al., 1987) also enhance postauricular reflex magnitude; any of these maneuvers can help separate the postauricular reflex from other potentials recorded at similar sites (Mahendran et al., 2007).

Postauricular reflex magnitude increases with the volume of the acoustic probe (Fox, Peyton, & Ragi, 1989; Purdy, Agung, Hartley, Patuzzi, & O’Beirne, 2005; Thornton, 1975; Yoshie & Okudaira, 1969); they are also elicited by white noise clicks at 65 decibels (dB) lasting 100 microseconds, whereas blink reflexes are not, indicating that the two reflexes are elicited by qualitatively different sounds (Aaron & Benning, 2016). Postauricular reflex thresholds correlate strongly with audiometric thresholds (e.g., .97 in Thornton, 1975); the reflex habituates neither across the duration of audiometric recording sessions (Purdy et al., 2005) nor across thousands of serially presented clicks (Fox et al., 1989; Yoshie & Okudaira, 1969) or startle probes (Hackley et al., 2017) as long as they are spaced at least 100 ms apart. Using headphones with extended high-frequency response and rising chirps (which allow low-frequency information to be integrated over the basilar membrane of the cochlea) to elicit the reflex instead of white noise clicks further enhances postauricular reflex magnitude (Agung, Purdy, Patuzzi, O’Beirne, & Newall, 2005). Combined, these methods for recording the postauricular reflex make it a useful screening tool for hearing problems that compares favorably to other audiometric tools (McCaslin, Jacobson, & Harry, 2008), particularly when sampled at 2,000 Hz or higher to prevent distortion of the signal (Thornton, 1975).

Attention

The postauricular reflex has been used in a growing number of attention studies in humans. Postauricular reflexes are larger behind the ear to which attention is directed in an auditory detection task (Hackley et al., 1987), indicating that attention can modulate the magnitude of this reflex. The magnitude of the postauricular reflex is also attenuated if the reflex-eliciting noise probe is preceded by the occurrence of a transient acoustic stimulus (prepulse)—an effect known as prepulse inhibition (Hackley, 1993; Hackley et al., 1987; Hebert, Valle-Inclán, & Hackley, 2015). Prepulse inhibition is thought to reflect a low-level sensory gating mechanism that affords “protection” at early stages of perceptual processing (Braff, Geyer, & Swerdlow, 2001; Fendt, Li, & Yeomans, 2001; Graham, 1975). However, the postauricular reflex appears less subject to controlled attentional influences than the startle blink. Attending to the prepulse enhances prepulse inhibition of the startle blink reflex but not of the postauricular reflex (Hackley et al., 1987). This dissociation reflects the faster, simpler circuitry of the postauricular reflex (Hackley, 1993; Sollers & Hackley, 1997). In contrast, simple visual gratings generate prepulse facilitation for startle probes 300 ms after the grating’s onset (Hackley et al., 2017). This pattern is akin to that found for the ipsilateral R1 trigeminal blink reflex elicited by cutaneous stimulation, which also has an onset latency of ~10 ms. The R1 blink facilitates the latency of the more typical bilateral R2 blink (onset latency ~25–40 ms) that closes the eyelid with the same motor units as the R1 (Dengler, Rechl, & Struppler, 1982) and exhibits prepulse inhibition at least 1,000 ms after prepulse offset (Ison, Sanes, Foss, & Pinckney, 1990).

Continued attention to visual and auditory foregrounds inhibits postauricular reflex magnitude, and more complex foreground stimuli generate more postauricular reflex inhibition. Postauricular reflexes are typically smaller during picture processing than while watching a fixation cross during intertrial intervals (Benning, Patrick, & Lang, 2004), and they are smallest during the processing of long, dynamic sounds (Benning, 2011). Both pictures and sounds appear to inhibit postauricular reflex magnitude compared to reflexes collected while participants view a simple geometric cue indicating the valence of an upcoming stimulus (Molina, Ait Oumeziane, & Benning, 2014). Thus, the apparent prepulse facilitation of the postauricular reflex during the first 500 ms of picture presentation (Aaron & Benning, 2016) may instead reflect the development of prepulse inhibition while foreground stimuli are processed. Overall, sustained attention to cross-modal foreground stimuli inhibits postauricular reflex magnitude less than attention to same-modal foreground stimuli. Increasing cognitive load also decreases postauricular reflex magnitude (Parks, Hilimire, & Corballis, 2009), whereas the startle blink reflex appears potentiated during high cognitive loads (Thorne, Dawson, & Schell, 2006). In all, a variety of prepulse methods demonstrate that the postauricular reflex is modulated by attention differently than the typical startle blink reflex, suggesting that they arise from separable neurobiological mechanisms.

Emotion

The postauricular reflex also serves as an index of positive emotion. The initial study of emotional modulation of the postauricular reflex revealed that postauricular reflexes are larger during pleasant pictures (or potentiated) than during neutral or aversive pictures, a pattern evidenced by over 70% of the sample (Benning, Patrick, & Lang, 2004). Subsequent research found similar potentiations during pleasant sounds (Benning, 2011) and video clips (Sparks & Lang, 2010) compared to neutral or aversive sounds or videos. However, potentiation of the postauricular reflex appears more robust during pictures than during sounds (Benning, 2011). This effect is also present during active experimental paradigms. Postauricular reflexes are potentiated during the offset of pain-inducing stimuli (Franklin, Lee, Hanna, & Prinstein, 2013) and during stimuli participants know not to be associated with shock during aversive conditioning (Benning, Bernat, Starr, Gewirtz, & Patrick, 2004). Given the potentiation of the postauricular reflex during appetitive and relief-from-shock stimuli, it is unlikely that Preyer’s reflex is an animal analog of this reflex, as Preyer’s reflex is potentiated during stimuli signaling threat (Cassella & Davis, 1986). Overall, the postauricular reflex assesses positive emotion during multiple types of stimuli across genders and races (Aaron & Benning, 2016; Benning, 2011; Sparks & Lang, 2010).

Only the postauricular reflex is larger during pleasant stimuli, as the anterior auricular muscle does not appear to be activated by acoustic probes, and the superior auricular reflex is not consistently modulated by emotion (Benning, 2011). These results suggest that efferent activity from the postauricular branch of the facial nerve, which uniquely innervates the postauricular muscle compared to the superior and auricular muscles (Sataloff & Selber, 2003), is responsible for this reflex and its modulation. Furthermore, modulation of the startle blink is uncorrelated with that of the postauricular reflex (Aaron & Benning, 2016; Hackley, Muñoz, Hebert, Valle-Inclán, & Vila, 2009; Sandt et al., 2009), indicating that the two reflexes index separable appetitive and defensive processes, respectively. The inhibition of the postauricular reflex during aversive stimuli is not as consistent as its potentiation during pleasant stimuli. Indeed, postauricular reflexes during aversive pictures are not inhibited compared to those during neutral pictures throughout the course of picture processing (Aaron & Benning, 2016). This pattern contrasts with the attentional inhibition of the startle blink reflex during pleasant versus neutral pictures, which starts within 300 ms of pleasant picture onset and lasts throughout the course of picture processing (Bradley, Codispoti, & Lang, 2006).

Content, intensity, and anticipation.

The influence of stimulus content on postauricular reflex modulation has been examined across nine studies (Aaron & Benning, 2016; Benning, 2011; Benning, Patrick, & Lang, 2004; Gable & Harmon-Jones, 2009; Hackley et al., 2009; Hebert, Valle-Inclán, & Hackley, 2015; Quevedo et al., 2015; Quevedo, Benning, Gunnar, & Dahl, 2009; Sandt et al., 2009). Seven of these presented enough information to permit tabulation of effects for specific contents, and five of these reported enough statistical detail to permit computing Cohen’s d effect sizes; not all studies included all picture contents described below. Postauricular reflexes were potentiated for erotica in 6/6 studies (average d across 3 studies = 0.44), for food in 6/7 studies (average d across 5 studies = 0.38), for nurturant pictures in 4/5 studies (average d across 3 studies = 0.29), and for adventure pictures in 2/6 studies (average d = 0.07). Effect sizes for all but adventure contents were at least small. Attractive opposite-sex people potentiated postauricular reflexes in 2/2 studies (d in 1 study = 0.51), but nature scenes potentiated postauricular reflexes in 0/1 studies with no computable effect size.

Thus, erotica and food seem to be the most potent potentiators of postauricular reflex magnitude, indicating that this reflex indexes appetitive drives (Sandt et al., 2009). Human faces can also modulate postauricular reflexes, but only female happy expressions potentiate the reflex compared to neutral faces; postauricular reflexes during angry faces do not differ from those during neutral faces, irrespective of the face’s sex (Hess, Sabourin, & Kleck, 2007). Furthermore, both pictures (Benning, Patrick, & Lang, 2004; cf. Gable & Harmon-Jones, 2009) and videos (Sparks & Lang, 2010) high in arousal generate stronger modulation of the postauricular reflex than those low in arousal. In sum, a number of emotional stimulus characteristics influence postauricular reflex modulation.

Thus far, studies have concentrated on consummatory positive emotional processing, which refers to emotional processing during the experience of pleasant stimuli themselves. A burgeoning literature is beginning to address whether postauricular reflexes are modulated during anticipatory positive emotional processing as well, suggesting that the postauricular reflex may assess “wanting” as well as “liking” (Berridge, Robinson, & Aldridge, 2009). When participants have their gaze directed toward food they are about to eat as rewards or punishments for task performance, postauricular reflexes are larger when anticipating a chocolate reward than a banana peel punishment (Hackley et al., 2009). However, this sort of anticipatory processing employs the same kinds of visual stimuli that picture-viewing studies use to assess consummatory processing. There is no modulation of postauricular reflex magnitude in studies either using blank screens during a 6 second period in anticipation of an appetizing food picture reward (Hebert et al., 2015) or using geometric cues associated with pleasant pictures more broadly (Molina et al., 2014). A similar lack of emotional modulation during anticipation periods characterizes the startle blink reflex (Dichter, Tomarken, & Baucom, 2002; Riesel, Weinberg, Moran, & Hajcak, 2013), so these reflexes likely only assess consummatory emotional processing.

Development, individual differences, and psychopathology.

The development of postauricular reflex potentiation has been examined in a small number of studies detailed below. Children from families with relatively high levels of socioeconomic status show potentiation of the postauricular reflex only in mid- to late puberty; this is not the case for such children who are prepubertal or in early puberty (Quevedo et al., 2015; Quevedo et al., 2009). However, children who suffered early adversity but were adopted by families with high levels of socioeconomic status had a reverse pattern, in which they showed potentiation of the postauricular reflex during early puberty but not during mid- to late puberty (Quevedo et al., 2015). It is unclear whether this pattern reflects a dampening of positive emotional processing in such children as they mature, or if instead it represents a delayed transition from normal positive emotional processing to a transient period of positive emotional blunting that resolves with further development. Postauricular reflexes are also larger overall for children who suffered early adversity than those who did not, a pattern that is evident for the startle blink reflex (Quevedo et al., 2015).

A number of individual differences in positive emotion are related to postauricular reflex potentiation. In mid- to late pubertal adolescents, it is associated with self-reported trait levels of positive emotionality and interpersonal affiliation (Quevedo et al., 2009). Within psychopathologies, individuals with objective binge-eating episodes show larger postauricular reflex potentiation specifically during pictures of food compared to those without such episodes (Racine, Hebert, & Benning, 2018). Individuals with autism spectrum disorder show increased potentiation of the postauricular reflex during aversive versus neutral pictures, indicating that they have abnormal processing of aversive picture contents (Dichter, Benning, Holtzclaw, & Bodfish, 2010).

The postauricular reflex is also sensitive to psychopathologies featuring anhedonia, which signifies a lack of positive emotion. Both undergraduates with subclinical levels of depression (Benning & Ait Oumeziane, 2017; cf. Sloan & Sandt, 2010) and clinically depressed community participants with anhedonic symptoms of depression (Benning & Mercado, 2015) have reduced potentiation of the postauricular reflex during a picture-viewing paradigm. Individuals diagnosed with schizophrenia also show deficits in postauricular reflex potentiation, and these deficits relate to the severity of the negative symptoms of the disorder (which include anhedonia; Bitner, Benson, Nichols, Park, & Benning, 2012). However, whereas depressed individuals do not show inhibited startle blink potentiation during aversive versus neutral pictures (Benning & Ait Oumeziane, 2017; Benning & Mercado, 2015; Sloan & Sandt, 2010; cf. Dichter & Tomarken, 2008; Vaidyanathan, Welo, Malone, Burwell, & Iacono, 2014), those with schizophrenia do (Bitner et al., 2012). Opiate-dependent participants demonstrate both reduced postauricular reflex potentiation and smaller overall postauricular reflex magnitude while viewing a variety of pictures (Lubman et al., 2009).

Assembling Neural Mechanisms of Postauricular Reflex Activity

Bottom-up vestigial pinna activity.

One animal model of rat pinna activity during acoustic startle parses the reflex into a direct disynaptic cochlear root—medial facial nucleus connection (through the trapezoid body) and an indirect trisynaptic connection between these two areas through the nRPC (Horta-Júnior, López, Alvarez-Morujo, & Bittencourt, 2008). The direct connection may represent the animal analog of the postauricular reflex (Hackley, 2015), particularly if Horta-Júnior et al. (2008) used the caudal portion of the levator auris longus muscle, which represents the best homolog of the postauricular muscle in humans (note 34 of Table 2 in Diogo et al., 2008). However, this direct pathway sends output only to the ipsilateral medial facial nerve nucleus, but postauricular reflexes are elicited bilaterally even with unilateral stimulation (hence the former moniker “crossed acoustic response” for this reflex; Douek et al., 1973). Thus, neural activity earlier in this circuit must reflect the point at which acoustic stimuli are processed bilaterally before the nRPC.

In humans, auditory information from the ventral cochlear nucleus appears to split onto the ipsilateral ventral nucleus of the trapezoidal body and contralateral medial nucleus of the trapezoidal body, which aids in localizing sounds (Kulesza & Grothe, 2015). Thus, the model entails activity proceeding from the cochlea → ventral cochlear nucleus → trapezoid body bilateralization → medial facial nucleus → postauricular branch of the facial nerve → postauricular muscle. This model permits the postauricular reflex to remain separate from the elaborative processing of the startle circuit, which generates responses throughout the body to a variety of stimuli as opposed to just the ears (Kızıltan, Gündüz, & Şahin, 2010). Back projections from the trapezoidal body onto ventral cochlear root neurons in this circuit are also uniquely implicated in prepulse inhibition with interstimulus intervals up to 200 ms (Gómez-Nieto et al., 2014). Nevertheless, it is unclear whether longer interstimulus intervals would lead to the prepulse facilitation observed in Hackley et al. (2017).

Top-down left frontal activity.

The brain circuitry that contributes to postauricular reflex potentiation during positive emotional states has yet to be studied. In collaboration with Rebecca Ray, Thomas Armstrong, and David Zald, I examined the neural correlates of postauricular reflex modulation in a sample of 26 women who participated in a two-part picture-viewing study to examine which brain regions’ activity correlated with postauricular reflex potentiation. In the first session, they watched 48 pictures from the International Affective Picture System (Lang, Bradley, & Cuthbert, 2008) depicting pleasant adventure, erotic, food, and nurturant contents; neutral buildings, humans, landscapes, and objects; and aversive scenes of contamination, moral violations, mutilation, and threat. These normative ratings of these pictures were balanced such that pleasant and aversive pictures were equidistant from neutral pictures on valence and arousal. A 50 ms, 105 dB white noise probe with near-instantaneous rise time was delivered 3, 4, or 5 s after the onset of each picture that was analyzed; 4 pictures were not probed to reduce the probe’s predictability.

I used a within-subjects multivariate analysis of variance to analyze within-subjects z scored postauricular reflex magnitude (defined as the maximum activity 8–35 ms after probe onset minus mean postauricular EMG activity 50 ms before the probe). I conducted follow-up Helmert contrasts, which tested postauricular reflex magnitude during pleasant versus neutral and aversive pictures and that during neutral versus aversive pictures. I also conducted paired t tests of postauricular reflexes during each content minus those during the aggregate of all neutral contents. Like in Aaron & Benning (2016), pleasant and aversive valences assessed as the average of these content-neutral contrasts had greater reliabilities (Cronbach’s αpleasant-neutral = .35, αaversive-neutral = .54) than those using postauricular reflex magnitudes within each valence alone, which were both less than −1. These α values are low but consistent with those found in previous research (Aaron & Benning, 2016). I used a critical α level of .05 for all comparisons.

In the second session, participants watched 144 pictures with similar contents during a functional magnetic resonance imaging (fMRI) session. Data from two women in the first phase were excluded due to excessive motion artifacts (n = 1) or repeated program crashes (n = 1). To avoid generating motion artifacts, noise probes were not delivered during this session; I also did not use softer clicks to elicit postauricular reflexes in the scanner due to the relatively large amount of ambient noise that could not be eliminated sufficiently with headphones. Using SPM5 software, I applied a mask to analyze only brain regions with greater blood oxygenation level dependent (BOLD) responses during pleasant than neutral pictures. I only considered clusters of at least 12 contiguous 8 cubic millimeter voxels that correlated with postauricular reflex potentiation at a threshold of p < .005, which was sufficient to create a cluster-wise p < .05.

The Postauricular Reflex as a Measure of Attention and Positive EmotionClick to view larger

Figure 1 Postauricular reflex magnitudes by picture valence and ear. Inset panel: Postauricular reflex modulation for each picture content minus neutral. Cohen’s d is reported underneath each content’s bar. Error bars represent the standard error of the mean (N = 26). * p < .05, ** p < .01.

Figure by Stephen D. Benning (2017); available at https://dx.doi.org/10.6084/m9.figshare.4233125 under a CC-BY4.0 license.

Findings from the psychophysiological session are depicted in Figure 1. Emotion modulated postauricular reflex magnitude. Postauricular reflexes during pleasant pictures were larger than those during neutral or aversive pictures, F(1,25) = 19.0, p < .001, η2p = .43, and those during neutral and aversive pictures did not differ from each other, F(1,25) = 1.75, p = .197, η2p = .07. There were no effects involving ear on postauricular reflex magnitude. Thus, postauricular reflex magnitudes were collapsed across ear for the remaining analyses. Only postauricular reflexes during nurturant and adventure pictures were greater than those during neutral pictures. No picture content inhibited postauricular reflex magnitude relative to that during neutral pictures, which followed the inconsistency noted above of the inhibition of postauricular reflex magnitude during aversive pictures.

The Postauricular Reflex as a Measure of Attention and Positive EmotionClick to view larger

Figure 2 Left frontal brain regions correlated with potentiation of the postauricular reflex during pleasant versus neutral pictures (N = 24).

Figure by Stephen D. Benning (2016); available at https://dx.doi.org/10.6084/m9.figshare.4233104 under a CC-BY4.0 license.

Results from the fMRI session are depicted in Figure 2. BOLD activity in the left middle frontal (kE = 13, p = .039, maximum t(23) = 3.70) and left inferior frontal cortex (kE = 15, p = .028, maximum t(23) = 3.59) correlated with postauricular reflex potentiation. These results comport well with the notion that left frontal brain activity is associated with positive emotional processing (Davidson, Shackman, & Maxwell, 2004; De Pascalis, Cozzuto, Caprara, & Alessandri, 2013).

Conclusion

The Postauricular Reflex as a Measure of Attention and Positive EmotionClick to view larger

Figure 3 Posterior view of a pseudo-3D model of neural activity that generates (lower half) and potentiates (upper half) postauricular reflex magnitude during pleasant versus neutral emotional states. Spiral = cochlea, VCN = ventral cochlear nucleus, VNTB = ventral nucleus of the trapezoid body, MNTB = medial nucleus of the trapezoid body, MFN = medial facial nucleus, PAM = postauricular muscle, IFG = inferior frontal gyrus (left), and MFG = middle frontal gyrus (left). Back projections from the VNTB to the VCN (not diagrammed) are also implicated in prepulse inhibition of the postauricular reflex.

Figure by Natosha D. Benning and Stephen D. Benning (2017); available at https://dx.doi.org/10.6084/m9.figshare.4233098 under a CC-BY4.0 license. Adapted from Morecraft et al. (2001).

From this study, a possible model for the neural circuitry that underpins postauricular reflex potentiation takes shape, which is diagrammed in Figure 3. Tracings of facial nerve efferents in rhesus monkeys reveal that Brodmann’s area (BA) 6 controls the auricular musculature, whereas subregions of BA23 control the muscles around the eye that would be involved in generating the startle blink (Cattaneo & Pavesi, 2014). BA6 also contains the area in the middle frontal gyrus that is associated with postauricular reflex potentiation during pleasant versus neutral pictures. Thus, activity from left inferior frontal regions may feed into the left middle frontal gyrus, which then traverses a number of pathways to synapse on the medial facial nerve nucleus within the pons (Morecraft, Louie, Herrick, & Stilwell-Morecraft, 2001; Morecraft et al., 2004). From there, activity propagates to the postauricular branch of the facial nerve and into the postauricular muscle, whose reflexive activity is amplified from this input when a noise probe or click elicits it. It appears that for pictures, this circuit requires at least 2,500 ms from picture onset to activate (Aaron & Benning, 2016), suggesting that this pathway entails substantial cortical elaborative processing (Pessoa & Adolphs, 2010). Whether postauricular reflex potentiation can occur more quickly for stimuli that are less perceptually complex—yet equally as motivating to attention (Lang, Bradley, & Cuthbert, 1997)—remains to be examined.

Future Directions

  1. (1) Is the postauricular reflex a measure of positive emotion or approach processing? Because anger is also associated with left frontal activity, it may be more appropriate to consider this pattern of activation as reflecting approach processing instead of positive emotion (De Pascalis et al., 2013; Harmon-Jones, Gable, & Peterson, 2010). One key emotional state that could help to resolve this conundrum is anger, a negative emotional state that is also associated with approach motivation and increased left frontal EEG activity (Harmon-Jones, 2003). To the extent that moral violations elicit angry emotional states, the results of the study reported above suggest that the postauricular reflex assesses positive emotion rather than approach processing, as moral violation pictures did not potentiate postauricular reflex magnitude. However, we did not assess whether these pictures indeed elicited anger; further work should use better-validated anger measures—including delivering shocks (Buss, 1961) or hot sauce (Lieberman, Solomon, Greenberg, & McGregor, 1999) to another person—to resolve this question.

  2. (2) What other processes modulate postauricular reflexes? Thus far, both positive emotion and relief from painful stimuli have been shown to potentiate postauricular reflexes. Therefore, more than appetitive emotional drives modulate postauricular reflex magnitudes. It is also clear that attention to complex perceptual foregrounds inhibits this reflex, as does directing attention to the ear in which an acoustic prepulse occurs along with engaging in cognitively demanding tasks. Beyond these psychological processes, the characteristics of the eliciting sounds, rotating the eyes toward the eliciting sound, and ongoing tension in flexed neck and head muscles can influence the magnitude of the postauricular reflex. Yet these may not exhaust the possible uses of the postauricular reflex in psychology, audiology, and anatomy. Measuring the postauricular reflex in any paradigm during which punctate noise probes are presented—whether clicks, tones, rising chirps, or phonemes (Agung et al., 2005)—could yield valuable information about other processes that modulate postauricular reflexes. Such paradigms could include auditory oddballs (Opitz, Mecklinger, Von Cramon, & Kruggel, 1999), change deafness (Gregg, Irsik, & Snyder, 2014), and stop signal tasks that employ tones as signals (Heritage & Benning, 2013). Studying such diverse paradigms would establish boundary conditions to understand how postauricular reflexes are modulated—or not—across paradigms.

  3. (3) What is the evolutionary basis for postauricular reflex modulation? Hackley (2015) advanced an elegant theory that the postauricular reflex comprises one portion of a multifaceted orienting system. Postauricular muscle activity is inhibited to increase hearing acuity during orienting to soft sounds (Stekelenburg & van Boxtel, 2001). This muscle’s activity is also increased when unexpected sounds incidental to a task are presented (Stekelenburg & van Boxtel, 2002). Therefore, postauricular reflex potentiation may reflect the orienting activity of other muscles that increase hearing acuity during orienting. Two such muscles are both involved in smiling (Ekman, Davidson, & Friesen, 1990), which increases overall postauricular reflex magnitude (Dus & Wilson, 1975; Patuzzi & O’Beirne, 1999): the zygomaticus major on the cheek and orbicularis oculi around the eye (Stekelenburg & van Boxtel, 2001).

However, several sets of findings argue against this theory. Mean zygomatic EMG activity is larger only during nurturant pictures as opposed to pleasant pictures generally (Bradley, Codispoti, Cuthbert, & Lang, 2001) and only functions this way at all in women (Bradley, Codispoti, Sabatinelli, & Lang, 2001). In contrast, postauricular reflex potentiation across a variety of picture contents is equally strong for men and women (Aaron & Benning, 2016; Sparks & Lang, 2010). Picture valence also does not affect baseline postauricular EMG magnitude (Benning, Patrick, & Lang, 2004), indicating that postauricular muscles are not influenced by putative crosstalk from other muscles during picture processing. Finally, postauricular reflex modulation does not correlate with modulation of zygomatic or orbicularis EMG activity during pictures (Aaron & Benning, 2016).

Ethological studies of primates revealed they have larger and more frequent auricular movements while foraging (Trivedi & Mohnot, 2002), and the postauricular reflex has shown relatively consistent potentiation while looking at food or its depictions (Aaron & Benning, 2016; Hackley et al., 2009; Hebert et al., 2015; Quevedo et al., 2009; Sandt et al., 2009). These results led to the nursing hypothesis, which advanced that postauricular reflex potentiation reflects the tendency of infant primates to retract their ears while nursing (Johnson, Valle-Inclán, Geary, & Hackley, 2012). In support of this hypothesis, participants who adopted a pursed-lip posture (similar to what would be used during nursing) showed postauricular reflex potentiation during pleasant versus neutral pictures, but those who adopted a grimace involving bared teeth did not (Johnson et al., 2012). However, the teeth-baring grimace may have caused a ceiling effect on postauricular reflex magnitude, as reflex magnitudes during this pose were greater than those during the lip-pursing pose. This study also did not include a “no facial manipulation” condition to examine whether the lip-pursing pose created a hyperpotentiation of the postauricular reflex compared to conditions used in previous postauricular reflex research.

Finally, stimulus contents beyond those associated with nursing potentiate the postauricular reflex, indicating that this reflex is sensitive to appetitive stimuli more broadly (Sandt et al., 2009). Indeed, Hanuman langurs also move their ears more frequently during play (Trivedi & Mohnot, 2002), and both rats (Finlayson, Lampe, Hintze, Würbel, & Melotti, 2016) and ruminant animals (Proctor & Carder, 2014; Reefmann, Bütikofer Kaszàs, Wechsler, & Gygax, 2009; Tamioso, Rucinque, Taconeli, da Silva, & Molento, 2017) hold their ears backward (compared to upright or forward) while feeding or being stroked, which should require postauricular muscle activity. Thus, the postauricular reflex may represent the last vestige of auricular activity expressing broad positive emotion in species with reduced facial expressivity (Reefmann et al., 2009) or visual acuity (Finlayson et al., 2016). In this light, primates’ increased visual acuity and facial reactivity may have reduced the selective disadvantage of less functional auricular musculature, eventually permitting humans to have purely vestigial postauricular activity linked to positive emotion. Future work should examine whether backward ear positions in these (and other) species are even more pronounced during high-arousal rewarding behaviors—particularly mating, cues of which are potent potentiators of postauricular reflexes in humans. Furthermore, the ambiguous meaning of backward ear poses in carnivorous species, like dogs (Bloom & Friedman, 2013; Racca, Guo, Meints, & Mills, 2012), suggests the link between backward-pointed ears and positive emotion deserves examination across species.

References

Aaron, R. V., & Benning, S. D. (2016). Postauricular reflexes elicited by soft acoustic clicks and loud noise probes: Reliability, prepulse facilitation, and sensitivity to picture contents. Psychophysiology, 53(12), 1900–1908. https://doi.org/10.1111/psyp.12757.Find this resource:

Agung, K., Purdy, S. C., Patuzzi, R. B., O’Beirne, G. A., & Newall, P. (2005). Rising-frequency chirps and earphones with an extended high-frequency response enhance the post-auricular muscle response. International Journal of Audiology, 44(11), 631–636.Find this resource:

Benning, S. D. (2011). Postauricular and superior auricular reflex modulation during emotional pictures and sounds. Psychophysiology, 48(3), 410–414. https://doi.org/10.1111/j.1469-8986.2010.01071.x.Find this resource:

Benning, S. D., & Ait Oumeziane, B. (2017). Reduced positive emotion and underarousal are uniquely associated with subclinical depression symptoms: Evidence from psychophysiology, self-report, and symptom clusters. Psychophysiology, 54(7), 1010–1030. https://doi.org/10.1111/psyp.12853.Find this resource:

Benning, S. D., Bernat, E., Starr, M. J., Gewirtz, J. C., & Patrick, C. J. (2004). Post-auricular reflex potentiation during relief stimuli in differential aversive conditioning: A construct validation study. Psychophysiology, 41, S3–S4.Find this resource:

Benning, S. D., & Mercado, K. (2015). Consummatory and anticipatory emotional deficits in depression. Psychophysiology, 52, S101.Find this resource:

Benning, S. D., Patrick, C. J., & Lang, A. R. (2004). Emotional modulation of the post-auricular reflex. Psychophysiology, 41(3), 426–432. https://doi.org/10.1111/j.1469-8986.00160.x.Find this resource:

Berridge, K. C., Robinson, T. E., & Aldridge, J. W. (2009). Dissecting components of reward: “liking,” “wanting,” and learning. Current Opinion in Pharmacology, 9(1), 65–73. https://doi.org/10.1016/j.coph.2008.12.014.Find this resource:

Bérzin, F., & Fortinguerra, C. R. (1993). EMG study of the anterior, superior and posterior auricular muscles in man. Annals of Anatomy = Anatomischer Anzeiger: Official Organ of the Anatomische Gesellschaft, 175(2), 195–197.Find this resource:

Bickford, R. G., Jacobson, J. L., & Cody, D. T. R. (1964). Nature of average evoked potentials to sound and other stimuli in man. Annals of the New York Academy of Sciences, 112(1), 204–218. https://doi.org/10.1111/j.1749-6632.1964.tb26749.x.Find this resource:

Bitner, H. D., Benson, T., Nichols, H. S., Park, S., & Benning, S. D. (2012). Schizophrenia and the potentiation of the postauricular reflex: A study on emotion. Young Scientist, 2, 49–50.Find this resource:

Bloom, T., & Friedman, H. (2013). Classifying dogs’ (Canis familiaris) facial expressions from photographs. Behavioural Processes, 96, 1–10. https://doi.org/10.1016/j.beproc.2013.02.010.Find this resource:

Bochenek, W., & Bochenek, Z. (1976). Postauricular (12 msec latency) responses to acoustic stimuli in patients with peripheral, facial nerve palsy. Acta Oto-Laryngologica, 81(3–4), 264–269.Find this resource:

Bradley, M. M., Codispoti, M., Cuthbert, B. N., & Lang, P. J. (2001). Emotion and motivation I: Defensive and appetitive reactions in picture processing. Emotion, 1(3), 276–298. https://doi.org/10.1037/1528-3542.1.3.276.Find this resource:

Bradley, M. M., Codispoti, M., & Lang, P. J. (2006). A multi‐process account of startle modulation during affective perception. Psychophysiology, 43(5), 486–497. https://doi.org/10.1111/j.1469-8986.2006.00412.x.Find this resource:

Bradley, M. M., Codispoti, M., Sabatinelli, D., & Lang, P. J. (2001). Emotion and motivation II: Sex differences in picture processing. Emotion, 1(3), 300. https://doi.org/10.1037/1528-3542.1.3.300Find this resource:

Braff, D. L., Geyer, M. A., & Swerdlow, N. R. (2001). Human studies of prepulse inhibition of startle: Normal subjects, patient groups, and pharmacological studies. Psychopharmacology, 156(2–3), 234–258. https://doi.org/10.1007/s002130100810.Find this resource:

Buss, A. H. (1961). The Psychology of Aggression. New York: Wiley.Find this resource:

Cassella, J. V., & Davis, M. (1986). Habituation, prepulse inhibition, fear conditioning, and drug modulation of the acoustically elicited pinna reflex in rats. Behavioral Neuroscience, 100(1), 39–44. https://doi.org/10.1037/0735-7044.100.1.39.Find this resource:

Cattaneo, L., & Pavesi, G. (2014). The facial motor system. Neuroscience & Biobehavioral Reviews, 38, 135–159. https://doi.org/10.1016/j.neubiorev.2013.11.002.Find this resource:

Cody, D. T. R., & Bickford, R. G. (1969). Averaged evoked myogenic responses in normal man. The Laryngoscope, 79(3), 400–416. https://doi.org/10.1288/00005537-196903000-00007.Find this resource:

Cody, D. T. R., Bickford, R. G., & Klass, D. W. (1969). Averaged evoked myogenic responses in normal man. International Audiology, 8(2–3), 391–397. https://doi.org/10.3109/05384916909079084.Find this resource:

Cody, D. T. R., Jacobson, J. L., Walker, J. C., & Bickford, R. G. (1964). Averaged evoked myogenic and cortical potentials to sound in man. Annals of Otology, Rhinology & Laryngology, 73(3), 763–777. https://doi.org/10.1177/000348946407300315.Find this resource:

Cook, A., & Patuzzi, R. (2014). Rotation of the eyes (not the head) potentiates the postauricular muscle response. Ear and Hearing, 35(2), 230–235. https://doi.org/10.1097/AUD.0b013e3182a4efdf.Find this resource:

Davidson, R. J., Shackman, A. J., & Maxwell, J. S. (2004). Asymmetries in face and brain related to emotion. Trends in Cognitive Sciences, 8(9), 389–391. https://doi.org/10.1016/j.tics.2004.07.006.Find this resource:

Davis, H., Engebretson, M., Lowell, E. L., Satterfield, J., & Yoshie, N. (1964). Evoked responses to clicks recorded from the human scalp. Annals of the New York Academy of Sciences, 112(1), 224–225. https://doi.org/10.1111/j.1749-6632.1964.tb26751.x.Find this resource:

Davis, H., Lowell, E. L., & Goldstein, R. (1965). Sonomotor reflexes: Myogenic evoked potentials. Acta Oto-Laryngologica. Supplementum, 206, 122–128.Find this resource:

Davis, M., Gendelman, D. S., Tischler, M. D., & Gendelman, P. M. (1982). A primary acoustic startle circuit: Lesion and stimulation studies. Journal of Neuroscience, 2(6), 791–805.Find this resource:

De Grandis, D., & Santoni, P. (1980). The post-auricular response: A single motor unit study. Electroencephalography and Clinical Neurophysiology, 50(5–6), 437–440.Find this resource:

De Meirsman, J., Claes, G., & Geerdens, L. (1980). Normal latency value of the facial nerve with detection in the posterior auricular muscle and normal amplitude value of the evoked action potential. Electromyography and Clinical Neurophysiology, 20(6), 481–485.Find this resource:

De Pascalis, V., Cozzuto, G., Caprara, G. V., & Alessandri, G. (2013). Relations among EEG-alpha asymmetry, BIS/BAS, and dispositional optimism. Biological Psychology, 94(1), 198–209. https://doi.org/10.1016/j.biopsycho.2013.05.016.Find this resource:

Dengler, R., Rechl, F., & Struppler, A. (1982). Recruitment of single motor units in the human blink reflex. Neuroscience Letters, 34(3), 301–305. https://doi.org/10.1016/0304-3940(82)90192-6.Find this resource:

Dichter, G. S., Benning, S. D., Holtzclaw, T. N., & Bodfish, J. W. (2010). Affective modulation of the startle eyeblink and postauricular reflexes in autism spectrum disorder. Journal of Autism and Developmental Disorders, 40(7), 858–869. https://doi.org/10.1007/s10803-009-0925-y.Find this resource:

Dichter, G. S., & Tomarken, A. J. (2008). The chronometry of affective startle modulation in unipolar depression. Journal of Abnormal Psychology, 117(1), 1–15. https://doi.org/10.1037/0021-843X.117.1.1.Find this resource:

Dichter, G. S., Tomarken, A. J., & Baucom, B. R. (2002). Startle modulation before, during and after exposure to emotional stimuli. International Journal of Psychophysiology, 43(2), 191–196.Find this resource:

Diogo, R., Abdala, V., Lonergan, N., & Wood, B. A. (2008). From fish to modern humans—comparative anatomy, homologies and evolution of the head and neck musculature. Journal of Anatomy, 213(4), 391–424. https://doi.org/10.1111/j.1469-7580.2008.00953.x.Find this resource:

Diogo, R., & Wood, B. (2011). Soft-tissue anatomy of the primates: Phylogenetic analyses based on the muscles of the head, neck, pectoral region and upper limb, with notes on the evolution of these muscles. Journal of Anatomy, 219(3), 273–359. https://doi.org/10.1111/j.1469-7580.2011.01403.x.Find this resource:

Douek, E., Gibson, W., & Humphries, K. (1973). The crossed acoustic response. Journal of Laryngology & Otology, 87(8), 711–726. https://doi.org/10.1017/S0022215100077550.Find this resource:

Dus, V., & Wilson, S. J. (1975). The click-evoked post-auricular myogenic response in normal subjects. Electroencephalography and Clinical Neurophysiology, 39(5), 523–525.Find this resource:

Ekman, P., Davidson, R. J., & Friesen, W. V. (1990). The Duchenne smile: Emotional expression and brain physiology: II. Journal of Personality and Social Psychology, 58(2), 342–353. https://doi.org/10.1037/0022-3514.58.2.342.Find this resource:

Fendt, M., Li, L., & Yeomans, J. S. (2001). Brain stem circuits mediating prepulse inhibition of the startle reflex. Psychopharmacology, 156(2–3), 216–224. https://doi.org/10.1007/s002130100794.Find this resource:

Finlayson, K., Lampe, J. F., Hintze, S., Würbel, H., & Melotti, L. (2016). Facial indicators of positive emotions in rats. PLOS ONE, 11(11), e0166446. https://doi.org/10.1371/journal.pone.0166446.Find this resource:

Fox, J. E., Peyton, M. B., & Ragi, E. (1989). Lability of the postauricular and inion microreflexes, studied in the normal human subject. Electroencephalography and Clinical Neurophysiology, 72(1), 48–58. https://doi.org/10.1016/0013-4694(89)90030-8.Find this resource:

Franklin, J. C., Lee, K. M., Hanna, E. K., & Prinstein, M. J. (2013). Feeling worse to feel better: Pain-offset relief simultaneously stimulates positive affect and reduces negative affect. Psychological Science, 24(4), 521–529. https://doi.org/10.1177/0956797612458805.Find this resource:

Gable, P. A., & Harmon-Jones, E. (2009). Postauricular reflex responses to pictures varying in valence and arousal. Psychophysiology, 46(3), 487–490. https://doi.org/10.1111/j.1469-8986.2009.00794.x.Find this resource:

Gómez-Nieto, R., Sinex, D. G., Horta-Júnior, J. de A. C., Castellano, O., Herrero-Turrión, J. M., & López, D. E. (2014). A fast cholinergic modulation of the primary acoustic startle circuit in rats. Brain Structure and Function, 219(5), 1555–1573. https://doi.org/10.1007/s00429-013-0585-8.Find this resource:

Graham, F. K. (1975). The more or less startling effects of weak prestimulation. Psychophysiology, 12(3), 238–248.Find this resource:

Gregg, M. K., Irsik, V. C., & Snyder, J. S. (2014). Change deafness and object encoding with recognizable and unrecognizable sounds. Neuropsychologia, 61, 19–30. https://doi.org/10.1016/j.neuropsychologia.2014.06.007.Find this resource:

Guerra, A. B., Metzinger, S. E., Metzinger, R. C., Xie, C., Xie, Y., Rigby, P. L., & Naugle, T. (2004). Variability of the postauricular muscle complex: Analysis of 40 hemicadaver dissections. Archives of Facial Plastic Surgery, 6(5), 342–347. https://doi.org/10.1001/archfaci.6.5.342.Find this resource:

Hackley, S. A. (1993). An evaluation of the automaticity of sensory processing using event-related potentials and brain-stem reflexes. Psychophysiology, 30(5), 415–428.Find this resource:

Hackley, S. A. (2015). Evidence for a vestigial pinna-orienting system in humans. Psychophysiology, 52(10), 1263–1270. https://doi.org/10.1111/psyp.12501.Find this resource:

Hackley, S. A., Muñoz, M. A., Hebert, K., Valle-Inclán, F., & Vila, J. (2009). Reciprocal modulation of eye-blink and pinna-flexion components of startle during reward anticipation. Psychophysiology, 46(6), 1154–1159. https://doi.org/10.1111/j.1469-8986.2009.00867.x.Find this resource:

Hackley, S. A., Ren, X., Underwood, A., & Valle-Inclán, F. (2017). Prepulse inhibition and facilitation of the postauricular reflex, a vestigial remnant of pinna startle. Psychophysiology, 54(4), 566–577. https://doi.org/10.1111/psyp.12819.Find this resource:

Hackley, S. A., Woldorff, M., & Hillyard, S. A. (1987). Combined use of microreflexes and event-related brain potentials as measures of auditory selective attention. Psychophysiology, 24(6), 632–647. https://doi.org/10.1111/j.1469-8986.1987.tb00343.x.Find this resource:

Harmon-Jones, E. (2003). Clarifying the emotive functions of asymmetrical frontal cortical activity. Psychophysiology, 40(6), 838–848. https://doi.org/10.1111/1469-8986.00121.Find this resource:

Harmon-Jones, E., Gable, P. A., & Peterson, C. K. (2010). The role of asymmetric frontal cortical activity in emotion-related phenomena: A review and update. Biological Psychology, 84(3), 451–462. https://doi.org/10.1016/j.biopsycho.2009.08.010.Find this resource:

Hebert, K. R., Valle-Inclán, F., & Hackley, S. A. (2015). Modulation of eyeblink and postauricular reflexes during the anticipation and viewing of food images. Psychophysiology, 52(4), 509–517. https://doi.org/10.1111/psyp.12372.Find this resource:

Heritage, A. J., & Benning, S. D. (2013). Impulsivity and response modulation deficits in psychopathy: Evidence from the ERN and N1. Journal of Abnormal Psychology, 122(1), 215–222. https://doi.org/10.1037/a0030039.Find this resource:

Hess, U., Sabourin, G., & Kleck, R. E. (2007). Postauricular and eyeblink startle responses to facial expressions. Psychophysiology, 44(3), 431–435. https://doi.org/10.1111/j.1469-8986.2007.00516.x.Find this resource:

Hitchcock, J., & Davis, M. (1986). Lesions of the amygdala, but not of the cerebellum or red nucleus, block conditioned fear as measured with the potentiated startle paradigm. Behavioral Neuroscience, 100(1), 11–22. https://doi.org/10.1037/0735-7044.100.1.11.Find this resource:

Horta-Júnior, J. de A. C., López, D. E., Alvarez-Morujo, A. J., & Bittencourt, J. C. (2008). Direct and indirect connections between cochlear root neurons and facial motor neurons: Pathways underlying the acoustic pinna reflex in the albino rat. Journal of Comparative Neurology, 507(5), 1763–1779. https://doi.org/10.1002/cne.21625.Find this resource:

Ison, J. R., Sanes, J. N., Foss, J. A., & Pinckney, L. A. (1990). Facilitation and inhibition of the human startle blink reflexes by stimulus anticipation. Behavioral Neuroscience, 104(3), 418–429.Find this resource:

Jacobson, J. L., Cody, D. T., Lambert, E. H., & Bickford, R. G. (1964). Physiological properties of the post-auricular response (sonomotor) in man. Physiologist, 7(3), 167.Find this resource:

Johnson, G. M., Valle-Inclán, F., Geary, D. C., & Hackley, S. A. (2012). The nursing hypothesis: An evolutionary account of emotional modulation of the postauricular reflex. Psychophysiology, 49(2), 178–185. https://doi.org/10.1111/j.1469-8986.2011.01297.x.Find this resource:

Kiang, N. Y. S., Crist, A. H., French, A. H., & Edwards, A. G. (1963). Postauricular electrical response to acoustic stimuli in humans. Quarterly progress report no: 68. Research Laboratory of Electronics, Massachusetts Institute of Technology.Find this resource:

Kızıltan, M. E., Gündüz, A., & Şahin, R. (2010). Auditory evoked blink reflex and posterior auricular muscle response: Observations in patients with HFS and PFS. Journal of Electromyography and Kinesiology, 20(3), 508–512. https://doi.org/10.1016/j.jelekin.2009.07.009.Find this resource:

Kulesza, R. J., & Grothe, B. (2015). Yes, there is a medial nucleus of the trapezoid body in humans. Frontiers in Neuroanatomy, 9. https://doi.org/10.3389/fnana.2015.00035.Find this resource:

Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1997). Motivated attention: Affect, activation, and action. In P. J. Lang, R. F. Simons, & M. Balaban (Eds.), Attention and Orienting: Sensory and Motivational Processes (pp. 97–135). Mahwah, NJ: Lawrence Erlbaum Associates.Find this resource:

Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (2008). International affective picture system (IAPS): Affective ratings of pictures and instruction manual. Technical Report A-8. University of Florida, Gainesville, FL.Find this resource:

Lee, Y., López, D. E., Meloni, E. G., & Davis, M. (1996). A primary acoustic startle pathway: Obligatory role of cochlear root neurons and the nucleus reticularis pontis caudalis. Journal of Neuroscience, 16(11), 3775–3789.Find this resource:

Lieberman, J. D., Solomon, S., Greenberg, J., & McGregor, H. A. (1999). A hot new way to measure aggression: Hot sauce allocation. Aggressive Behavior, 25(5), 331–348. https://doi.org/10.1002/(SICI)1098-2337(1999)25:5<331::AID-AB2>3.0.CO;2-1.Find this resource:

Lubman, D. I., Yücel, M., Kettle, J. W. L., Scaffidi, A., Mackenzie, T., Simmons, J. G., & Allen, N. B. (2009). Responsiveness to drug cues and natural rewards in opiate addiction: Associations with later heroin use. Archives of General Psychiatry, 66(2), 205–212. https://doi.org/10.1001/archgenpsychiatry.2008.522.Find this resource:

Mahendran, S., Bleeck, S., Winter, I. M., Baguley, D. M., Axon, P. R., & Carlyon, R. P. (2007). Human auditory nerve compound action potentials and long latency responses. Acta Oto-Laryngologica, 127(12), 1273–1282. https://doi.org/10.1080/00016480701253086.Find this resource:

McCaslin, D. L., Jacobson, G. P., & Harry, T. (2008). The recordability of two sonomotor responses in young normal subjects. Journal of the American Academy of Audiology, 19(7), 542–547.Find this resource:

Mishra, J., Martinez, A., Sejnowski, T. J., & Hillyard, S. A. (2007). Early cross-modal interactions in auditory and visual cortex underlie a sound-induced visual illusion. Journal of Neuroscience, 27(15), 4120–4131. https://doi.org/10.1523/JNEUROSCI.4912-06.2007.Find this resource:

Molina, S. M., Ait Oumeziane, B., & Benning, S. D. (2014). Postauricular and startle blink reflexes assess consummatory but not anticipatory emotional processing. Psychophysiology, 51, S15.Find this resource:

Morecraft, R. J., Louie, J. L., Herrick, J. L., & Stilwell-Morecraft, K. S. (2001). Cortical innervation of the facial nucleus in the non-human primate. Brain, 124(1), 176–208. https://doi.org/10.1093/brain/124.1.176.Find this resource:

Morecraft, R. J., Stilwell-Morecraft, K. S., & Rossing, W. R. (2004). The motor cortex and facial expression: New insights from neuroscience. The Neurologist, 10(5), 235–249.Find this resource:

O’Beirne, G. A., & Patuzzi, R. B. (1999). Basic properties of the sound-evoked post-auricular muscle response (PAMR). Hearing Research, 138(1–2), 115–132.Find this resource:

Opitz, B., Mecklinger, A., Von Cramon, D. Y., & Kruggel, F. (1999). Combining electrophysiological and hemodynamic measures of the auditory oddball. Psychophysiology, 36(1), 142–147. https://doi.org/10.1017/S0048577299980848.Find this resource:

Parks, N. A., Hilimire, M. R., & Corballis, P. M. (2009). Visual perceptual load modulates an auditory microreflex. Psychophysiology, 46(3), 498–501.Find this resource:

Patuzzi, R. B., & O’Beirne, G. A. (1999). Effects of eye rotation on the sound-evoked post-auricular muscle response (PAMR). Hearing Research, 138(1–2), 133–146.Find this resource:

Pessoa, L., & Adolphs, R. (2010). Emotion processing and the amygdala: From a “low road” to “many roads” of evaluating biological significance. Nature Reviews Neuroscience, 11(11), 773–783. https://doi.org/10.1038/nrn2920.Find this resource:

Proctor, H. S., & Carder, G. (2014). Can ear postures reliably measure the positive emotional state of cows? Applied Animal Behaviour Science, 161, 20–27. https://doi.org/10.1016/j.applanim.2014.09.015.Find this resource:

Purdy, S. C., Agung, K. B., Hartley, D., Patuzzi, R. B., & O’Beirne, G. A. (2005). The post-auricular muscle response: An objective electrophysiological method for evaluating hearing sensitivity. International Journal of Audiology, 44(11), 625–630.Find this resource:

Quevedo, K., Johnson, A. E., Loman, M. M., Lafavor, T., Moua, B., & Gunnar, M. R. (2015). The impact of early neglect on defensive and appetitive physiology during the pubertal transition: a study of startle and postauricular reflexes. Developmental Psychobiology, 57(3), 289–304. https://doi.org/10.1002/dev.21283.Find this resource:

Quevedo, K. M., Benning, S. D., Gunnar, M. R., & Dahl, R. E. (2009). The onset of puberty: Effects on the psychophysiology of defensive and appetitive motivation. Development and Psychopathology, 21(1), 27–45. https://doi.org/10.1017/S0954579409000030.Find this resource:

Racca, A., Guo, K., Meints, K., & Mills, D. S. (2012). Reading faces: Differential lateral gaze bias in processing canine and human facial expressions in dogs and 4-year-old children. PLOS ONE, 7(4), e36076. https://doi.org/10.1371/journal.pone.0036076.Find this resource:

Racine, S. E., Hebert, K. L., & Benning, S. D. (2018). Emotional reactivity and appraisal of food in relation to eating disorder cognitions and behaviours: Evidence to support the motivational conflict hypothesis. European Eating Disorders Review, 26(1), 3–10. https://doi.org/10.1002/erv.2567Find this resource:

Reefmann, N., Bütikofer Kaszàs, F., Wechsler, B., & Gygax, L. (2009). Ear and tail postures as indicators of emotional valence in sheep. Applied Animal Behaviour Science, 118(3–4), 199–207. https://doi.org/10.1016/j.applanim.2009.02.013.Find this resource:

Riesel, A., Weinberg, A., Moran, T., & Hajcak, G. (2013). Time course of error-potentiated startle and its relationship to error-related brain activity. Journal of Psychophysiology, 27(2), 51–59. https://doi.org/10.1027/0269-8803/a00093.Find this resource:

Sandt, A. R., Sloan, D. M., & Johnson, K. J. (2009). Measuring appetitive responding with the postauricular reflex. Psychophysiology, 46(3), 491–497.Find this resource:

Sataloff, R. T., & Selber, J. C. (2003). Phylogeny and embryology of the facial nerve and related structures. Part II: Embryology. ENT: Ear, Nose & Throat Journal, 82(10), 764–779.Find this resource:

Serra, G., Tugnoli, V., Cristofori, M. C., Eleopra, R., & De Grandis, D. (1986). The electromyographic examination of the posterior auricular muscle. Electromyography and Clinical Neurophysiology, 26(8), 661–665.Find this resource:

Sloan, D. M., & Sandt, A. R. (2010). Depressed mood and emotional responding. Biological Psychology, 84(2), 368–374. https://doi.org/10.1016/j.biopsycho.2010.04.004.Find this resource:

Sollers, J. J., & Hackley, S. A. (1997). Effects of foreperiod duration on reflexive and voluntary responses to intense noise bursts. Psychophysiology, 34(5), 518–526.Find this resource:

Sparks, J. V., & Lang, A. (2010). An initial examination of the post-auricular reflex as a physiological indicator of appetitive activation during television viewing. Communication Methods and Measures, 4(4), 311–330. https://doi.org/10.1080/19312458.2010.527872.Find this resource:

Stekelenburg, J. J., & van Boxtel, A. (2001). Inhibition of pericranial muscle activity, respiration, and heart rate enhances auditory sensitivity. Psychophysiology, 38(4), 629–641. https://doi.org/10.1111/1469-8986.3840629.Find this resource:

Stekelenburg, J. J., & van Boxtel, A. (2002). Pericranial muscular, respiratory, and heart rate components of the orienting response. Psychophysiology, 39(6), 707–722. https://doi.org/10.1111/1469-8986.3960707.Find this resource:

Tamioso, P. R., Rucinque, D. S., Taconeli, C. A., da Silva, G. P., & Molento, C. F. M. (2017). Behavior and body surface temperature as welfare indicators in selected sheep regularly brushed by a familiar observer. Journal of Veterinary Behavior: Clinical Applications and Research, 19, 27–34. https://doi.org/10.1016/j.jveb.2017.01.004.Find this resource:

Thorne, G. L., Dawson, M. E., & Schell, A. M. (2006). Effects of perceptual load on startle reflex modification at a long lead interval. Psychophysiology, 43(5), 498–503. https://doi.org/10.1111/j.1469-8986.2006.00420.x.Find this resource:

Thornton, A. R. (1975). Distortion of averaged post-auricular muscle responses due to system bandwidth limits. Electroencephalography and Clinical Neurophysiology, 39(2), 195–197.Find this resource:

Thornton, A. R. D. (1975). The use of post-auricular muscle responses. Journal of Laryngology & Otology, 89(10), 997–1010. https://doi.org/10.1017/S0022215100081317.Find this resource:

Trivedi, S., & Mohnot, S. M. (2002). Functional status of pinna muscles in Hanuman langur, Semnopithecus entellus: Speculation on functional loss of pinna muscles in humans. Primate Report, 63, 41–48.Find this resource:

Vaidyanathan, U., Welo, E. J., Malone, S. M., Burwell, S. J., & Iacono, W. G. (2014). The effects of recurrent episodes of depression on startle responses. Psychophysiology, 51(1), 103–109. https://doi.org/10.1111/psyp.12152.Find this resource:

Yoshie, N., & Okudaira, T. (1969). Myogenic evoked potential responses to clicks in man. Acta Oto-Laryngologica, 67(sup252), 89–103. https://doi.org/10.3109/00016486909120515.Find this resource: