week 11 Flashcards
(27 cards)
What is measured by the motion coherence task?
It measures the ability to extract a coherent motion signal from noise by determining the threshold at which motion direction can be reliably detected.
How does the direction integration task differ from the motion coherence task?
In the direction integration task, difficulty is increased by broadening the range of motion directions, testing the ability to pool or average directional information rather than merely segregate signal from noise.
Which conditions have been found to exhibit elevated motion coherence thresholds?
Elevated thresholds have been reported in conditions such as Williams Syndrome, autism, dyslexia, hemiplegia, Fragile X Syndrome, schizophrenia, and in some cases of congenital cataract.
What does the magnocellular hypothesis suggest regarding dyslexia?
It proposes that dyslexic individuals experience deficits in the magnocellular pathway—which is critical for processing high temporal frequencies—leading to elevated motion coherence thresholds.
What supporting evidence is mentioned for a magnocellular deficit in dyslexia?
Evidence includes anatomical findings of reduced cell size in magnocellular layers of the LGN and behavioral studies showing elevated motion coherence thresholds, though only about 30% of dyslexics exhibit these difficulties.
How does the weak central coherence theory explain motion perception differences in autism?
It suggests that autistic individuals tend to integrate fewer visual details, resulting in reduced global pooling and a higher reliance on local information, which may lead to elevated motion thresholds.
What neural factors might contribute to atypical motion perception in autism?
Factors include reduced long-range functional connectivity, enhanced local processing, and diminished top-down modulation during sensory integration.
What information does equivalent noise modeling provide in these tasks?
It estimates two key parameters: internal noise (accuracy of local estimates) and the number of samples or extent of global pooling used in integrating motion signals.
How are differences in internal noise and sampling thought to differ between dyslexia and autism?
Dyslexia is often linked to increased internal noise affecting motion signal estimation, while autism may involve increased sampling—indicating broader pooling over local signals.
What is meant by the “dorsal stream vulnerability” account?
This account suggests that the dorsal visual pathway, which processes motion and spatial information, is more susceptible to developmental anomalies across various conditions.
What primary functions are associated with the dorsal stream?
The dorsal stream (the “where” or “action” pathway) is responsible for processing motion, spatial location, and guiding actions based on visual input.
What defines visual stress according to the lecture?
Visual stress refers to discomfort, perceptual distortions, or even pain when viewing certain patterns or contrasts that deviate from natural scene statistics.
What types of stimuli are common triggers for visual stress?
Common triggers include repeating, high‐contrast striped patterns (especially around 3 cycles per degree), certain color contrasts (e.g., red–green), and flickering images.
What is the Pattern Glare Test and how is it used?
The Pattern Glare Test presents patterned stimuli at a set distance while the participant focuses on a central point. They then report any distortions or discomfort, helping to quantify visual stress.
How do migraine and photosensitive epilepsy relate to visual stress?
Both conditions are associated with heightened sensitivity to triggering stimuli like high-contrast patterns and flicker, which can provoke severe discomfort, auras, or even seizures.
What role do colored overlays/tinted lenses play in dyslexia, as discussed in the lecture?
They are sometimes used to reduce visual stress by modifying cortical excitability, although evidence for their broad effectiveness remains inconclusive.
How might increased cortical excitability contribute to visual discomfort?
When the visual cortex is challenged by stimuli that stray from natural patterns (e.g., stripes or intense flicker), it may become overactive, leading to discomfort or perceptual distortions.
What overarching conclusion does the lecture suggest regarding visual differences across conditions?
While elevated motion coherence thresholds and visual stress are seen across various conditions, their underlying causes may differ—highlighting the need to consider both shared mechanisms and condition-specific processes.
What proportion of dyslexic individuals is reported to show difficulties with motion perception, and why is this significant?
Approximately 30% of dyslexic people display difficulties with motion perception. This suggests that while atypical magnocellular function may contribute to dyslexia, it does not affect all individuals with the condition uniformly, highlighting the heterogeneity of the visual deficits.
What methodological challenges are associated with using the motion coherence task to assess magnocellular function?
The motion coherence task may not isolate magnocellular functioning exclusively because it also involves later processing stages in the dorsal stream. As a result, elevated thresholds could be due to factors beyond early magnocellular deficits, such as impaired signal integration or noise segregation.
Describe the procedure for administering the Pattern Glare Test and outline its key safety considerations.
The test begins by familiarizing the patient with a checklist of potential distortions using Pattern 1. The patient is then instructed to fixate on a central dot at about 40 cm for 5 seconds before reporting any distortions—such as bending, blurring, flicker, fading, or shadowy shapes—and noting whether these occur uniformly or more on one side. Safety is crucial since certain patterns (notably Pattern 2) can provoke adverse reactions (e.g., nausea, dizziness, or even seizures in photosensitive individuals).
What specific perceptual distortions and symptoms are assessed during the Pattern Glare Test?
The test records distortions like unusual colors, bending or blurring of lines, shimmering or flickering effects, fading, and the appearance of shadowy shapes. It also asks whether these distortions are symmetric or more pronounced on one side.
How does equivalent noise modeling distinguish between internal noise and sampling in motion perception tasks, and why is this distinction important?
Equivalent noise modeling estimates two parameters: internal noise (the imprecision in processing individual motion signals) and sampling (the number of visual samples integrated into a global percept). This distinction is crucial because it helps determine if elevated motion thresholds are due to noisy local processing or a reduction in effective integration of visual information.
What insights do altered EEG measures (e.g., in the N1/N2 components) provide regarding visual processing in migraineurs exposed to varying chromaticity separations?
Changes in the N1/N2 components suggest that as chromaticity separation increases, migraineurs exhibit heightened cortical responses—indicative of cortical hyper-excitability—which correlate with increased discomfort compared to those without migraines.
