Evidence for differential top-down and bottom-up suppression in posterior parietal cortex

Area of Science:

• Neuroscience
• Cognitive Science
• Visual Perception

Background:

• The lateral intraparietal area (LIP) is implicated in guiding visual search behavior.
• Previous research indicates reduced neural responses to irrelevant stimuli and previously fixated items during search.

Purpose of the Study:

• To investigate the distinct neural mechanisms underlying suppressed responses to distractors versus previously fixated targets in visual search.
• To differentiate between bottom-up and top-down processing contributions to behavioral guidance in the LIP.

Main Methods:

• Neural activity and local field potentials (LFPs) were recorded in the LIP of two animals performing a visual foraging task.
• Animals searched for a target among identical potential targets and irrelevant distractors.
• Stimuli included novel distractors and previously fixated targets within the response field.

Main Results:

• LFP power in the alpha and low beta bands was elevated when previously fixated targets were in the LIP response field.
• LFP power did not differ significantly between novel potential targets and distractors.
• Single-unit responses to distractors were reduced, suggesting bottom-up processing.

Conclusions:

• Reduced responses to novel distractors likely result from bottom-up, feed-forward processing in earlier visual areas.
• Reduced responses to previously fixated targets are attributed to active top-down suppression mechanisms within the LIP.
• These findings highlight distinct neural strategies for ignoring irrelevant information and re-engaging with previously encountered items during visual search.