Interpreting sensory and cognitive signals in the cortical reading network

Receptive field properties measured in the reading portion of the ventral occipital-temporal (VOT) cortex are task- and stimulus-dependent. To understand these effects, we analyzed responses in visual field-maps (V1-3, hV4, VO1) whose signals are likely inputs to the VOT. Within these maps, each voxel contains neurons that are responsive to specific regions of the visual field; these regions can be quantified using the moving bar paradigm and population receptive field (pRF) analysis. We measured pRFs using several types of contrast patterns within the bar (English words, Hebrew words, checkers, and false fonts). Word and false-font stimuli produce estimates that are as much as 3-4 deg closer to the fovea than checker stimuli in all visual field maps, becoming very pronounced in V3, hV4 and VO-1. The responses in the visual field maps suggest that the pRF shifts depend mostly on the visual characteristics of the stimulus, and may be explained by sensory signal models and their known neural circuitry. Responses in the VOT reading regions do not follow the same pattern as the visual maps. The pRF centers are confined to the central five degrees, and the responses to false-fonts differ from the responses to words. To understand these VOT signals, we suggest it is necessary to extend the sensory pRF model to include an explicit cognitive signal that distinguishes words from false-fonts.