Stimulus size modulates idiosyncratic neural face identity discrimination

Abstract

Humans show individual differences in neural facial identity discrimination (FID) responses across viewing positions. Critically, these variations have been shown to be reliable over time and to directly relate to observers' idiosyncratic preferences in facial information sampling. This functional signature in facial identity processing might relate to observer-specific diagnostic information processing. Although these individual differences are a valuable source of information for interpreting data, they can also be difficult to isolate when it is not possible to test many conditions. To address this potential issue, we explored whether reducing stimulus size would help decrease these interindividual variations in neural FID. We manipulated the size of face stimuli (covering 3°, 5°, 6.7°, 8.5°, and 12° of visual angle), as well as the fixation location (left eye, right eye, below the nasion, nose, and mouth) while recording electrophysiological responses. Same identity faces were presented with a base frequency of 6 Hz. Different identity faces were periodically inserted within this sequence to trigger an objective index of neural FID. Our data show robust and consistent individual differences in neural face identity discrimination across viewing positions for all face sizes. Nevertheless, FID was optimal for a larger number of observers when faces subtended 6.7° of visual angle and fixation was below the nasion. This condition is the most suited to reduce natural interindividual variations in neural FID patterns, defining an important benchmark to measure neural FID when it is not possible to assess and control for observers' idiosyncrasies.

Meta-analysis of experimental factors influencing single-pulse TMS effects on the early visual cortex

“…This intriguing phenomenon may also be attributed to spTMS preferentially activating neural populations with lower levels of activation, which reduces the signal-to-noise ratio (Silvanto and Muggleton, 2008). As visual angle of the stimulus decreased, the corresponding activated brain regions also decreased in size (Stacchi and Caldara, 2022). Consequently, when applying spTMS, it may disrupt the entire brain regions associated with a small stimulus but only affect part of the brain regions corresponding to a relatively large stimulus.…”