Training Transfers the Limits on Perception from Parietal to Ventral Cortex

• Published in: Current biology Vol. 24; no. 20; pp. 2445 - 2450
• Main Authors: Chang, Dorita H.F., Mevorach, Carmel, Kourtzi, Zoe, Welchman, Andrew E.
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 20.10.2014; Cell Press
• Subjects: Cerebral Cortex - physiology; Electrophysiological Phenomena; Humans; Learning; Neuroimaging; Psychomotor Performance - physiology; Transcranial Magnetic Stimulation; Visual Perception - physiology
• ISSN: 0960-9822; 1879-0445; 1879-0445
• DOI: 10.1016/j.cub.2014.08.058

Visually guided behavior depends on (1) extracting and (2) discriminating signals from complex retinal inputs, and these perceptual skills improve with practice [1]. For instance, training on aerial reconnaissance facilitated World War II Allied military operations [2]; analysts pored over stereoscopic photographs, becoming expert at (1) segmenting pictures into meaningful items to break camouflage from (noisy) backgrounds, and (2) discriminating fine details to distinguish V-weapons from innocuous pylons. Training is understood to optimize neural circuits that process scene features (e.g., orientation) for particular purposes (e.g., judging position) [3–6]. Yet learning is most beneficial when it generalizes to other settings [7, 8] and is critical in recovery after adversity [9], challenging understanding of the circuitry involved. Here we used repetitive transcranial magnetic stimulation (rTMS) to infer the functional organization supporting learning generalization in the human brain. First, we show dissociable contributions of the posterior parietal cortex (PPC) versus lateral occipital (LO) circuits: extracting targets from noise is disrupted by PPC stimulation, in contrast to judging feature differences, which is affected by LO rTMS. Then, we demonstrate that training causes striking changes in this circuit: after feature training, identifying a target in noise is not disrupted by PPC stimulation but instead by LO stimulation. This indicates that training shifts the limits on perception from parietal to ventral brain regions and identifies a critical neural circuit for visual learning. We suggest that generalization is implemented by supplanting dynamic processing conducted in the PPC with specific feature templates stored in the ventral cortex. •Before training, dorsal, but not ventral, rTMS disrupts perception in noisy displays•Training on fine differences boosts feature templates, facilitating detection in noise•After training, ventral, but not dorsal, rTMS becomes disruptive for targets in noise•Functional reweighting of dorsal and ventral circuits supports learning transfer Using TMS in human subjects, Chang et al. reveal differential roles of parietal and ventral cortex in extracting and discriminating visual targets, respectively. Training on fine discriminations causes a reweighting of the circuit: following learning, ventral, not parietal, activity determines target extraction task performance.