Parallel spatial channels converge at a bottleneck in anterior word-selective cortex

Area of Science:

• Neuroscience
• Cognitive Psychology
• Visual Perception

Background:

• The human visual system often encounters multiple objects simultaneously, particularly during reading.
• Behavioral studies indicate a serial bottleneck limits word recognition to one word at a time.

Purpose of the Study:

• To investigate how parallel visual processing channels converge into a serial bottleneck for word recognition using fMRI.
• To identify the neural mechanisms underlying the visual processing of multiple words.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was employed to study brain activity.
• Participants viewed simultaneous word pairs, with varying attentional demands.
• Activity in retinotopic cortex and word-selective regions (occipitotemporal sulcus, VWFA) was analyzed.

Main Results:

• Retinotopic cortex processed words in parallel across hemispheres.
• The left posterior visual word form area (VWFA) showed independent attentional modulation for words in both hemifields, supporting parallel processing.
• A more anterior region in the left hemisphere exhibited single-channel characteristics, consistent with a bottleneck.

Conclusions:

• The visual system supports parallel word processing up to a late stage in the ventral stream.
• A transition to a single processing channel in the left hemisphere underlies the behavioral bottleneck observed in reading.