Temporal limitations in object processing across the human ventral visual pathway

Temporal limitations in object processing across the human ventral visual pathway. J Neurophysiol 98: 382-393, 2007. First published May 9, 2007; doi: 10.1152/ jn.00568.2006. Behavioral studies have shown that object recognition becomes severely impaired at fast presentation rates, indicating a limitation in temporal processing capacity. Here, we studied whether this behavioral limit in object recognition reflects limitations in the temporal processing capacity of early visual areas tuned to basic features or high-level areas tuned to complex objects. We used functional MRI (fMRI) to measure the temporal processing capacity of multiple areas along the ventral visual pathway progressing from the primary visual cortex (V1) to high- level object- selective regions, specifically the fusiform face area (FFA) and parahippocampal place area (PPA). Subjects viewed successive images of faces or houses at presentation rates varying from 2.3 to 37.5 items/ s while performing an object discrimination task. Measures of the temporal frequency response profile of each visual area revealed a systematic decline in peak tuning across the visual hierarchy. Areas V1-V3 showed peak activity at rapid presentation rates of 18-25 items/ s, area V4v peaked at intermediate rates (9 items/s), and the FFA and PPA peakedat the slowest temporal rates (4-5 items/s). Our results reveal a progressive loss in the temporal processing capacity of the human visual system as information is transferred from early visual areas to higher areas. These data suggest that temporal limitations in object recognition likely result from the limited processing capacity of high-level object-selective areas rather than that of earlier stages of visual processing.