Aims: 

It is well known that configuration similarity of mask and target improves masking effect, but the role of categorical similarity is still unclear. The aim of our study was to investigate object recognition under forward masking with images that belong to the same or different category of objects. Special attention was paid to masking effect of faces with different emotional expression.

Methods: 

Thirty-eight healthy subjects with normal vision participated in the experiments. Sets of black and white drawings of animals, nonliving objects where used as tests (17 ms) and animals, nonliving objects and faces with threatens, fearful, happy, neutral expressions -as the masks (51 ms). The accuracy and reaction time (RT) were studied.

Results: 

The masking effect was the strongest in the experiments where the test and masking images belonged to the same category, and the recognition impairment was more marked for "animals" as compared to "objects". It is remarkable that faces did not influence effectively as masking stimuli, on the contrary they slightly accelerated the recognition and negative expressions seem to be more significant than happy and neutral ones. The type of facial expression correlated with RT but not with accuracy of recognition.

Conclusion: 

The observed effects are assumed to be determined by lateral inhibition. The contribution of this mechanism depends on the categorical proximity of the stimulus, and hence, their topographical neighborhood in the extrastriate visual cortex (Weber et al. 2009). The faces are not classical masks and probably mobilize processing resources and enhance spatial attention towards test stimuli. Reference: Weber, M., Thompson-Schill, S.L., Osherson, D., Haxby, J. & Parsons, L. 2009. Neuropsychologia 47, 859–868.