Parietal lesions produce illusory conjunction errors in rats

Raymond P Kesner

doi:10.3389/fnint.2012.00022

Abstract

When several different objects are presented, visual objects are perceived correctly only if their features are identified and then bound together. Illusory-conjunction errors result when an object is correctly identified but is combined incorrectly. The parietal cortex (PC) has been shown repeatedly to play an important role in feature binding. The present study builds on a series of recent studies that have made use of visual search paradigms to elucidate the neural system involved in feature binding. This experiment attempts to define the role the PC plays in binding the properties of a visual object that varies on the features of color and size in rats. Rats with PC lesions or control surgery were exposed to three blocks of 20 trials administered over a 1-week period, with each block containing 10-one feature and 10-two feature trials. The target object consisted of one color object (e.g., black and white) and one size object (e.g., short and tall). Of the 10 one feature trials, five of the trials were tailored specifically for size discrimination and five for color discrimination. In the two-feature condition, the animal was required to locate the targeted object among four objects with two objects differing in size and two objects differing in color. The results showed that the PC lesioned compared to control rats had difficulty in learning the one and two features components of the task and the rats also performed more poorly on the one vs. two feature components of the task. Based on a subsequent error analysis for color and size, the results showed a significant increase in illusory conjunction errors for the PC lesioned rats relative to controls for color and relative to color discrimination, suggesting that the PC may support feature binding as it relates to color. There was an increase in illusory conjunctions errors for both the PC lesioned and control animals for size, but this appeared to be due to highly variable performance with size discrimination. Overall these results suggest that the PC rats display performance errors that appear to be consistent with the notion of illusory conjunction errors.

Highlights

It has been suggested that the parietal cortex (PC) may play an important role in binding features of objects, objects, and places, as well as egocentric and allocentric spatial processing
Even though the control rats did not differ significantly in terms of the onevs. two-feature condition for shapes or color, there are data with humans showing that using shapes and color that parallel the findings with rats in that there was no significant difference in latency to respond to the one compared to the two-feature condition (Shafritz et al, 2002)
The data show that PC lesions in rats appear to disrupt acquisition of the task, which could be due to the difficulty in discriminating the features of the task, but in the first two blocks of trials, the PC lesioned rats do not show a deficit for the one-feature condition, but show a clear deficit for the two-feature condition suggesting that the PC may be involved in feature binding as reflected by illusory conjunction errors

Summary

Introduction

It has been suggested that the parietal cortex (PC) may play an important role in binding features of objects, objects, and places, as well as egocentric and allocentric spatial processing. The PC may be directly involved in perceptual binding between, for example, a shape and a color or a shape and a size requiring spatial attention Support for this idea comes from the performance of patient RM with bilateral PC damage, who had difficulty in tasks requiring binding shape and color or shape and size. The study was designed to develop an animal model of feature binding and determine whether PC lesions relative to sham lesions in rats result in the production of illusory conjunction errors using a visual search paradigm similar to the (Robertson et al, 1997) study with objects that varied either only on features of color or size (one feature) or the combination of color and size (two features)

Methods

Results

Conclusion