Adaptation aftereffects to facial expressions suppressed from visual awareness

Abstract

The study of adaptation aftereffects has been used as a tool to investigate the neural events that give rise to face perception. Recent adaptation studies suggest that face processing does not occur outside of awareness since identity- and gender-specific face aftereffects cannot be induced when the adapting face is rendered perceptually invisible using interocular suppression. However there is substantial evidence suggesting that facial expression, unlike identity and gender, is an attribute of faces that may recruit processes that are engaged automatically and independent of observers' awareness and attention. Therefore we investigated whether adaptation aftereffects specific to facial expressions could arise under continuous flash suppression (CFS). Our results show that adaptation to facial expressions is virtually abolished, when faces are suppressed from awareness. Moreover, this loss in aftereffect strength cannot be attributed to contrast adaptation exclusively, since results show only modest changes in perceived contrast following face adaptation. When observers endogenously attend to the location of the suppressed adapting stimulus, expression-specific aftereffects are enhanced. Our findings suggest that neural activity specifying affective information of facial expressions is highly vulnerable to the disruptive effect of interocular suppression, but that allocation of attentional resources can partially counteract suppression's effect.

Figure 1

Example of an adaptation trial in Experiment 1 using CFS to perceptually suppress the adapting face (e.g. face with happy expression). After the adaptation period and a brief interval, a test face (e.g. morphed face of happy and angry expressions) was presented dioptically. Observers subsequently judged the expression of the test face by pressing one of two response keys. Trials of other conditions consisted of a blank frame in place of the CFS display (visible condition) or in place of the adapting face (baseline condition).

Figure 2

Results of Experiment 1: The magnitude of FEAs when adapting faces were visible or invisible due to CFS. Aftereffect strength was determined as the difference in PSE acquired from baseline (no adaptation) and from adaptation conditions. Values near 0 indicate no effects of face adaptation on PSE estimates of the test face. Asterisks indicate the adaptation conditions where FEAs were significantly greater than 0, after adjusting for multiple comparisons (p < 0.006). There were two groups of observers, one where happy and angry expressions served as adapting stimuli (HA pair) and the other where angry and fearful expressions were adapting stimuli (AF pair). Morphs between adapting expressions served as test faces. Error bars represent SEM. FEA = facial expression aftereffect.

Figure 3

Results of Experiment 2: mean psychometric plots for 6 observers under conditions where CFS was present or absent during the adaptation period. Red and blue indicate conditions where an angry face or a happy face (respectively) was visible during the adaptation period. Pink and cyan indicate conditions where the adapting angry or happy face (respectively) was suppressed with CFS. Black is the mean performance for baseline conditions where no adapting face was present. Abscissa indicates the percentage of the happy expression in the morph test face where 0 is the angry expression. Ordinate displays the proportion of trials where observers’ judged the test face as being happy. Inset shows the mean magnitude of FEAs across participants for each adaptation condition, relative to baseline.

Figure 4

Results of Experiment 3. Change in apparent contrast (% RMS) of the test face relative to baseline when the adapting face was visible or rendered invisible by CFS. Error bars represent SEM. Asterisks within bars indicate conditions significantly differently from 0 and asterisks between bars indicate significant differences between conditions.

Figure 5

(A) Example of an adaptation trial in Experiment 4. Observers were cued to covertly attend to the left or right of fixation. During top-up adaptation, a happy face was presented in the cued location to the non-dominant eye while CFS images were presented in both locations to the dominant eye. A test face was briefly presented in the cued location and observers were to first respond to the expression of the test face and subsequently report the number of dimmed CFS frames (1 or 2) that had occurred during the adaptation period. (B) Experiment 4 results. FEA strength is plotted relative to baseline for each observer when performing an attention task in the location of a suppressed adapting face. First two data points on the left represent authors’ data. Error bars represent SEM.