Cortical interactions in vision and awareness: hierarchies in reverse

Area of Science:

• Neuroscience
• Visual Perception
• Cognitive Neuroscience

Background:

• Visual processing involves complex anatomical connections, including feedforward, feedback, and horizontal pathways between visual areas.
• Feedback projections, particularly from V5 to V1, are hypothesized to play a role in visual awareness and perception.

Purpose of the Study:

• To investigate the functional role of feedback projections in the visual cortex.
• To examine the contribution of V5-V1 feedback to visual awareness, stimulus detection, and visual motion priming.

Main Methods:

• Four experiments were conducted, including studies on a blindsight patient (GY).
• Techniques such as Transcranial Magnetic Stimulation (TMS) were employed to probe the timing and necessity of specific visual areas.
• Behavioral tasks assessed visual awareness, stimulus detection in visual search, and motion priming.

Main Results:

• Feedback projections from V5 to V1 were shown to be critical for visual awareness in a blindsight patient.
• The timing of V5-V1 interactions aligns with findings from single-unit physiology.
• V1 was found to be essential for stimulus detection, with TMS interference occurring late (up to 240 ms).
• The parietal cortex was not implicated in visual motion priming, whereas V5 was.

Conclusions:

• Feedback pathways, specifically V5 to V1, are vital for visual awareness and stimulus processing.
• The findings support recent physiological recordings and the reverse hierarchy theory of vision.
• The role of the parietal cortex in visual motion priming appears limited, with V5 being a key area.