Signal detection analysis of blindsight in monkeys.

Masatoshi Yoshida,Tadashi Isa

doi:10.1038/srep10755

Abstract

Macaque monkeys with a unilateral lesion in V1 have been used as an animal model of blindsight. While objective proof of blindsight requires that the two aspects of blindsight (residual forced-choice localization and attenuated yes-no detection) should be tested under identical stimulus conditions using bias-free measures of sensitivity, these have not been attained in studies of nonhuman primates. Here we tested two macaque monkeys with a unilateral V1 lesion with two saccade tasks using identical stimuli: a forced-choice (FC) task and a yes-no (YN) task. An analysis based on signal detection theory revealed that sensitivity in the FC task was significantly higher than that in the YN task. Such dissociation of sensitivity between the two tasks was not observed when near-threshold visual stimuli were presented in the normal, unaffected hemifield. These results suggest that the V1-lesioned monkeys resemble the well-studied blindsight patient G.Y., whose visual experience per se was completely abolished.

Highlights

Macaque monkeys with a unilateral lesion in V1 have been used as an animal model of blindsight
Two Japanese macaque monkeys were trained with the FC task and the YN task before the lesion
90% correct in the FC task suggests that the subject identified the saccadic target in 80% of the trials and selected the correct target in 10% of the trials by chance (50% of the 20% trials in which the subject did not identify the target). These results indicate that in about half of trials in the ST+ condition of the YN task, the monkeys performed as if it was the ST− condition of the YN task. These results show that the monkeys failed to detect the presence of the saccadic target (YN task), yet they succeeded in localizing the saccadic target in the forced choice condition (FC task)

Summary

Introduction

Macaque monkeys with a unilateral lesion in V1 have been used as an animal model of blindsight. An analysis based on signal detection theory revealed that sensitivity in the FC task was significantly higher than that in the YN task Such dissociation of sensitivity between the two tasks was not observed when near-threshold visual stimuli were presented in the normal, unaffected hemifield. These results suggest that the V1lesioned monkeys resemble the well-studied blindsight patient G.Y., whose visual experience per se was completely abolished. Previous studies showed that macaque monkeys with a unilateral lesion of V1 exhibit residual visual processing as demonstrated by key press, reaching or saccadic eye movements[2,3,4,5,6,7] These studies showed that the lesioned monkeys were able to discriminate or localize the visual stimuli presented in the contra-lesional visual field in a forced-choice (FC) task. We have identified a behavioural profile in monkeys that resemble blindsight in human subjects, including the well-studied patient G.Y. (see Discussion)

Methods

Results

Conclusion