Lecture 22 Flashcards
What is the difference in the number of areas involved in subcortical vision compared to cortical vision?
Subcortical vision involves fewer areas compared to cortical vision.
What is the primary target of the axons in the optic tract in cortical vision?
The retinogeniculostriate pathway is the target of approximately 90% of the axons in the optic tract.
Why do subcortical visual pathways exist, even though cortical visual pathways handle a significant portion of visual processing?
Subcortical visual pathways are phylogenetically older than cortical visual pathways, meaning they evolved before the cortical system.
What are the main differences between the subcortical and cortical visual systems?
Subcortical visual systems are older and may contribute to human experience and behavior, whereas cortical systems are more complex and evolved later.
What was the purpose of mapping the receptive fields of neurons in the superior colliculus?
The purpose was to map the receptive fields of neurons in the superficial layers of the superior colliculus.
How did researchers conduct the experiment to map the receptive fields in the superior colliculus?
Monkeys were trained to fixate a spot of light, and when they did, another stimulus was presented to determine the receptive field of the cell under study.
What did the mapping of receptive fields in the superior colliculus reveal?
It revealed that the superficial layers of the superior colliculus contain a retinotopic map of the visual field
What is the Sprague effect, and how does it relate to visual orienting responses?
The Sprague effect is the restoration of visual orienting responses in the cortically blind hemifield after removing the contralesional superior colliculus or cutting the fibers connecting the two superior colliculi.
What was initially thought to be the cause of the Sprague effect?
Mutual inhibition between the two superior colliculi was initially thought to cause the Sprague effect.
How did researchers compare the effects of disrupting cortical vision versus disrupting subcortical vision in rodents?
Rodents were trained to perform two tasks: a localization task and a discrimination task. Researchers then applied different lesions to the groups.
What was the result of disrupting subcortical vision in rodents on the localization and discrimination tasks?
Rodents with lesions affecting the superior colliculus performed normally in the localization task but were impaired in the discrimination task.
What is perimetry testing, and what does it reveal about cortical blindness in humans?
Perimetry testing maps the extent of scotomas (blind spots) in patients with cortical blindness. It shows that patients may not be aware of visual stimuli in regions represented by the damaged cortex.
What is the term used to describe residual vision in the absence of awareness in patients with cortical blindness?
This residual vision, which occurs without conscious awareness, is termed “blindsight.”
How does blindsight suggest that visual stimuli are processed in the absence of primary visual cortex?
Blindsight suggests that visual stimuli presented in the cortically blind hemifield are processed to some extent, even without awareness.
What pathway is hypothesized to be activated when stimuli appear within the cortically blind hemifield in blindsight patients?
The retinotectal pathway is hypothesized to be activated in blindsight patients when stimuli appear within the cortically blind hemifield.
