Emotional modulation of the postauricular reflex

Emotion and the post-auricular reflex 431
2000) and with motor deficits arising from Parkinson’s disease in
humans (Heim et al., 2002).
An alternative possibility is that increased post-auricular
reactivity reflects enhanced orienting to the noise probe stimulus.
Indeed, there is evidence that unexpected noises can evoke
observable movement of the post-auricular (pinna) muscle in
primates in whom this muscle serves more than a vestigial
function. Naturalistic observations of Hanuman langurs, a lower
primate species, have revealed that in adult males, loud and
surprising sounds yield brief (i.e., 0.2–0.3 s) movements of both
the pinna and the head in the direction of the noise (Trivedi &
Mohnot, 2002), suggesting that the pinna reflex serves an
orienting function in this primate species. It may be that states of
attentional engagement, such as those associated with viewing of
pleasurable pictures, facilitate this phasic reflexive orienting
reaction. However, because pleasant and unpleasant pictures
engage more attention than neutral (Lang et al., 1990, 1997), the
predicted attentional pattern would have been one of postauricular
reflex inhibition for both affective categories compared
to neutral. Furthermore, juveniles and females of this species
exhibit greater short-duration pinna movements primarily
during play, feeding, and foraging for food (Trivedi & Mohnot,
2002), suggesting heightened responsiveness of this reflexive
system specifically during pleasurable activities.
Nevertheless, there is evidence that unpleasant pictures also
engage attention (Lang et al., 1997), so it is possible that some
types of aversive pictures might likewise facilitate the postauricular
reflex. The current study focused on threat and physical
attack pictures that tend to be perceived as fearful. Modulatory
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REFERENCES
effects may differ for other aversive contents, such as sadness,
disgust, or mutilation pictures. It will also be important in future
research to examine effects for other pleasurable picture contents
(e.g., babies, animals, food). In addition, there are other
limitations of the current study that need to be addressed before
firm conclusions can be advanced regarding the post-auricular
reflex as an index of emotion. The current sample included only
men; thus, it will be important to replicate these findings in
women. Furthermore, it will be important to assess modulation
of the post-auricular reflex in emotional processing tasks other
than picture viewing. A key question is whether potentiation of
the post-auricular reflex would be observed in appetitive
conditioning or reward anticipation contexts, as is true for
startle in corresponding aversive paradigms (e.g., Hamm,
Greenwald, Bradley, & Lang, 1993; Patrick & Berthot, 1995).
Affirmative findings would lend support to the idea that the postauricular
reflex is primed during appetitive states. Finally, in light
of recent data indicating that hedonic valence and approach–
withdrawal aspects of emotion are dissociable, it would be
informative to assess whether the post-auricular reflex is
enhanced or inhibited during a negatively valent approach state
(e.g., anger; Harmon-Jones & Sigelman, 2001).
Notwithstanding these limitations, the findings of our study
are intriguing. They suggest that the post-auricular reflex, which
is evoked by the same acoustic probe as the startle reflex, may
provide an index of appetitive system activation. If so, this
reflexive measure could provide a valuable tool for studying basic
appetitive processes and investigating deficiencies in positive
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