fMRI- Adaptation reveals dissociable neural representations of identity and expression in face perception.
Winston, J.S., Henson, R.N.A., Fine-Goulden, & Dolan, R.J. (2004).
J. Neurophysiol. 92(3) 1830-1839.
Distributed model of face processing
‘Distributed model of face processing (Haxby JV, Hoffman EA, and Gobbini MI. The distributed human neural system for face perception. Trends Cogn Sci 4: 223–233, 2000) propose an anatomical dissociation between brain regions that encode invariant aspects of faces, such as identity, and those that encode changeable aspects of faces, such as expression’, p1 (KRO – but how can face be described as invariant there differences in profile perspective etc). Fits with Bruce & Young model.
Anatomical detail
Fusiform gyrus – identity of perceived face
Superior temporal sulcus (STS) represents ‘changeable aspects’ eg expression, gaze.
Single unit recoding in animals and data from patients with discrete lesions support both the concept of dissociation and the anatomical sites implicated. However studies have demonstrated enhanced fusiform activity to emotional faces. ‘This effect has been attributed to modulatory effects from amygdala, reflecting attentional processing associated with emotive stimuli’ (Dolan RJ. Emotion, cognition, and behavior. Science 298: 1191–1194, 2002).
Method
Using fMRI measures adaptation rather than difference. Adequately sampled regions of interest as follows fusiform, amygdala, STS, inferior frontal cortex, orbitofrontal cortex
5 male faces from Karolinski Directed Face database database contains two exemplars of each expression for each identity. Therefore could use different images of the same face for the adaption process. Stimuli were converted to grayscale and equated for mean luminance.
Expressions used – anger, disgust, fear, happiness and sadness
16 right handed healthy subjects, age 18-29, with normal vision. 2 rejected due to unacceptable level of fMRI artefact. Alongside the fMRI study a similar paradigm was used to test behavioral response in another cohort of 16 participants.
2x2 factorial design: Same identity (SI) Different identity (DI) Same expression (SE) Different expression (DE)
The effect of visual attention/arousal was monitored ‘there were no detectable differences in visual attention ( eye-gaze direction) or arousal (indexed by pupil diameter changes) between the different experimental conditions’ p8.
