Piecing it together: infants' neural responses to face and object structure

Abstract

Integration of local elements into a coherent global form is a fundamental aspect of visual object recognition. How the different hierarchically organized stages of visual analysis develop in order to support object representation in infants remains unknown. The aim of this study was to investigate structural encoding of natural images in 4- to 6-month-old infants and adults. We used the steady-state visual evoked potential (ssVEP) technique to measure cortical responses specific to the global structure present in object and face images, and assessed whether differential responses were present for these image categories. This study is the first to apply the ssVEP method to high-level vision in infants. Infants and adults responded to the structural relations present in both image categories, and topographies of the responses differed based on image category. However, while adult responses to face and object structure were localized over occipitotemporal scalp areas, only infant face responses were distributed over temporal regions. Therefore, both infants and adults show object category specificity in their neural responses. The topography of the infant response distributions indicates that between 4 and 6 months of age, structure encoding of faces occurs at a higher level of processing than that of objects.

Figure 1

Examples of stimulus frames used in the (a) face (KDEF identities AF14, AF13, AF19) and (b) object conditions of the experiment. Trials consisted of alternating scrambled and intact images at 3 Hz for 7 seconds. Decomposition of response waveforms into spectral harmonics isolated responses to the global structure of the intact image (1F; 3 Hz) from responses at the image update rate (2F; 6 Hz). Statistical analyses were conducted on the scalar amplitude of these harmonics.

Figure 2

Electrode groups used for analysis. Responses were calculated over left (light gray), middle (gray), and right (black) occipital scalp regions.

Figure 3

2D scalp topographic maps of adult (a) 1F and 2F responses to faces and objects (b) 1F-2F difference responses to faces and objects.

Figure 4

Mean amplitude of adult (a) 1F and (b) 2F responses to faces and objects. Error bars indicate standard errors of the mean. Asterisks indicate significant difference between conditions.

Figure 5

2D scalp topographic maps of infant (a) 1F and 2F responses to faces and objects and (b) 1F-2F difference responses to faces and objects.

Figure 6

Mean amplitude of infant (a) 1F and (b) 2F responses to faces and objects. Error bars indicate standard errors of the mean. Asterisk indicates significant difference between conditions (p < 0.06).