Blindsight? What is Blindsight?

Blindsight is a phenomenon in which people who are perceptually blind in a certain area of their visual field demonstrate some response to visual stimuli.

Usually observed in patients who have suffered major (usually hemianopic) field defects following damage to the striate cortex (V1) or to the optic radiation (which connect the lateral geniculate nucleus to the cortex).

Visual Pathway

2 Types of Blindsight ‘Type 1’ Blindsight: Visual ability of subjects without awareness. ‘Type II’ Blindsight: Characterized by residual visual abilities with awareness such as consciously detecting fast-moving stimulus and its direction or semantic priming from words in the blind field.

Type I blindsight demonstrates unconscious residual visual abilities that have been associated with a retinal-tectal pathway. This includes neuroendocrine responses such as melatonin suppression following exposure to a bright light, reflexive responses as shown by pupillary reaction to changes in illumination and implicit processing whereby presentation of a stimulus in the blind field affects performance in the normal visual field.

Type II blindsight patients possess some awareness of residual visual abilities such as target detection and localization by saccadic eye movements and manual pointing, movement direction detection, relative velocity discrimination, stimulus orientation detection, and/or semantic priming from words presented in the blind field.

Three Subcategories of Type 1 Blindsight Blindsight in Action: What Can the Different Sub-types of Blindsight Tell Us About the Control of Visually Guided Actions? James Danckert, Yves Rossetti

Blindsight Pathways Blindsight in Action: What Can the Different Sub-types of Blindsight Tell Us About the Control of Visually Guided Actions? James Danckert, Yves Rossetti

Blindsight Pathways

MRI of Hemispherectomized Patients Neural Substrates of Blindsight After Hemispherectomy Alain Ptito and Sandra E. Leh

fMRI Experiment

DTI in a Hemispherectomized Patient Neural Substrates of Blindsight After Hemispherectomy Alain Ptito and Sandra E. Leh

Humphreys Visual Field Analyser Can Blindsight Be Superior to ‘Sighted-sight’? Ceri T. Trevethan, Arash Sahraie, Larry Weiskrantz

Humphreys Visual Field Analyser Humphreys Visual Field Analyser

Blindsight is Not Degraded Normal Vision There can be selective loss of color but not for luminance Visible after images to unseen stimuli (“Prime-sight”) Super-sensitivity in the blind hemifield that is better than that of the intact hemifield. There can be a change in S-cone retinal inputs.

Color contrast processing in human striate cortex

Prime Sight in a Blindsight Subj Prime Sight in a Blindsight Subject (from Weiskrantz, Cowey, & Hodinott-Hill, 2002)

Super-sensitivity in the Blind Hemifield Can Blindsight Be Superior to ‘Sighted-sight’? Ceri T. Trevethan, Arash Sahraie, Larry Weiskrantz

The Absence of S-cone Input in the Blind Visual Field of Hemispherectomized Subjects Sandra E. Leh, Kathy T. Mullen and Alain Ptito

Spatial Summation Effect

Absence of S-cone Input in Human Blindsight Following Hemispherectomy Sandra E. Leh, Kathy T. Mullen, and Alain Ptito

Shape Discrimination Form Discrimination in a Case of Blindsight Ceri T. Trevethan, Arash Sahraie, Larry Weiskrantz

Identification of Low Contrast Object Images Form Discrimination in a Case of Blindsight Ceri T. Trevethan, Arash Sahraie, Larry Weiskrantz

Identification of Complex Objects Form Discrimination in a Case of Blindsight Ceri T. Trevethan, Arash Sahraie, Larry Weiskrantz

Reaching and Grasping as Indices of Visual Shape Perception Anthony J. Marcel

Reaching and Grasping as Indices of Visual Shape Perception Anthony J. Marcel

Structural descriptions of letters Blindsight and shape perception: deficit of visual consciousness or of visual function? Anthony J. Marcel

Illusory Contours Spanning the Sighted and Blind Fields Blindsight and shape perception: deficit of visual consciousness or of visual function? Anthony J. Marcel

After Images Blindsight and shape perception: deficit of visual consciousness or of visual function? Anthony J. Marcel

After Images

References: Absence of S-cone Input in Human Blindsight Following Hemispherectomy Sandra E. Leh, Kathy T. Mullen, and Alain Ptito Blindsight and Shape Perception: Deficit of Visual Consciousness or of Visual Function? Anthony J. Marcel Blindsight in Action: What Can the Different Sub-types of Blindsight Tell Us About the Control of Visually Guided Actions? James Danckert, Yves Rossetti Can Blindsight Be Superior to ‘Sighted-sight’? Ceri T. Trevethan, Arash Sahraie, Larry Weiskrantz Color Contrast Processing in Human Striate Cortex R. W. Kentridge, C. A. Heywood, and L. Weiskrantz Differential Pupillary Constriction and Awareness in the Absence of Striate Cortex L. Weiskrantz, A. Cowey, and J.L. Barbur Form Discrimination in a Case of Blindsight Ceri T. Trevethan, Arash Sahraie, Larry Weiskrantz Is Blindsight Just Degraded Normal Vision? Larry Weiskrantz Neural Substrates of Blindsight After Hemispherectomy Alain Ptito and Sandra E. Leh Prime-sight and Blindsight L. Weiskrantz