Differential affection of the visual information sub-streams in a patient with visual agnosia

TL;DR

A patient with visual agnosia shows impaired object recognition and grasping when color information is removed, highlighting the role of color processing in both visual streams.

Contribution

The study demonstrates how spared color processing in the ventral stream partially compensates for agnosia and contributes to visuomotor transformations in the dorsal stream.

Findings

The agnosic patient's recognition of color-masked objects was significantly worse than colored ones.

Color-masked objects led to larger kinematic impairments in the patient compared to controls.

Color processing in the ventral stream partially compensates for agnosia and supports visuomotor functions.

Abstract

Visual agnosia is a deficit of object recognition addressed to the damage of the ventral stream (VS). The dorsal stream (DS) is usually intact in these patients, and it can be derived from well-preserved reaching and grasping of visually presented objects. In this study, we presented a new case of a visual agnosic patient (AC) with an extensive lesion of the secondary visual cortex.

We examined the kinematics of his grasping behavior towards common day-to-day objects compared to a healthy control group. Both colored and color-masked objects were presented, and participants were instructed to grasp-then-name and name-then-grasp them.

The agnosic deficit was particularly evident when no color information was available to the patient: Although AC was able to recognize most colored objects with marked delay, his recognition of color-masked objects was very poor. Furthermore, the color-masked condition determined larger impairments in kinematic performance relative to the control group.

Results support the view that spared color processing in the VS allows for partial compensation of deficits. Color information is also processed along the DS, contributing to visuomotor transformations.

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