Segmentation precedes face categorization under suboptimal conditions

Carlijn Van Den Boomen,Johannes J Fahrenfort,Tineke M Snijders,Chantal Kemner

doi:10.3389/fpsyg.2015.00667

Abstract

Both categorization and segmentation processes play a crucial role in face perception. However, the functional relation between these subprocesses is currently unclear. The present study investigates the temporal relation between segmentation-related and category-selective responses in the brain, using electroencephalography (EEG). Surface segmentation and category content were both manipulated using texture-defined objects, including faces. This allowed us to study brain activity related to segmentation and to categorization. In the main experiment, participants viewed texture-defined objects for a duration of 800 ms. EEG results revealed that segmentation-related responses precede category-selective responses. Three additional experiments revealed that the presence and timing of categorization depends on stimulus properties and presentation duration. Photographic objects were presented for a long and short (92 ms) duration and evoked fast category-selective responses in both cases. On the other hand, presentation of texture-defined objects for a short duration only evoked segmentation-related but no category-selective responses. Category-selective responses were much slower when evoked by texture-defined than by photographic objects. We suggest that in case of categorization of objects under suboptimal conditions, such as when low-level stimulus properties are not sufficient for fast object categorization, segmentation facilitates the slower categorization process.

Highlights

Faces contain information of high ecological value: their presence and content hold important cues for behavior toward another person and the environment
We contrasted brain activity evoked by texture-defined faces versus houses and by objects versus homogeneous stimuli, and subsequently compared the moments at which these responses were maximal
Results showed the opposite: segmentation-related preceded category-selective responses evoked by texture-defined objects

Summary

Introduction

Faces contain information of high ecological value: their presence and content hold important cues for behavior toward another person and the environment. Two subprocesses that are essential for face perception are categorization and segmentation. Face categorization involves the process of placing an object in the specific category ‘faces’ and not in another one, such as ‘houses’ (Kanwisher et al, 1997; Epstein and Kanwisher, 1998). There is increasing evidence that successful categorization of a face in the brain is not sufficient for face perception. The temporal relation between categoryselective and segmentation-related responses in the brain is currently unclear. Increased insight in the temporal relation is crucial to understand face processing in typical adults, and in populations in which face processing has developed abnormally, since manipulations or abnormalities in the first process could affect the subsequent one as well. The current study investigates the temporal relation between face category-selective and segmentation-related responses in the adult brain

Methods

Results

Conclusion