Transcript What is 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
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 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
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