final exam Flashcards
What causes sensory illusions?
Caused by a limitation in how information is encoded
What causes perceptual illusions?
Brain misinterprets the sensory representation, often due to perceptual constancy or global interpretation
Define a bistable percept
An image that can be perceived in two ways, depending on what is interpreted as the figure and the background
How can results be skewed when using bistable percepts in experiments?
Some people have emotional responses to bistable percepts, which are linked to other cognitive processes, such as cognitive empathy. These responses can influence the target effect
Describe the perceptual shape constancy illusion
The brain’s tendency to assume the perceptual constancy in the physical attributes of an object causes a misinterpretation of a retinal image
What are the underlying processes that cause perceptual constancy illusions?
When producing a percept, the brain only has access to the retinal image during visual processing.
The retinal image is constantly changing when we move, therefore the brain actively interprets input in order to construct a stable percept
What can sensory illusions tell us about how the brain works?
- What brain cells are tuned to and what information cortical areas process
- How brain cells/areas interact
- How information is transformed across brain areas
What can perceptual illusions tell us about how the brain works?
- How the brain interprets sensory representations
- What assumptions the brain makes about the outside world
What does perceived size depend on?
The size of the retinal image and the (estimate of) viewing distance
The brain scales the size of the retinal image by an estimate of viewing distance to generate a percept size
What subconscious inference does the brain make when representing size constancy?
The distance to the object, which is then used to scale the retinal image accordingly at a subconscious level
Define the visual angle in regard to size perception
A measurement of how big a retinal image produced by an object is on the eye
Describe Holway and Boring’s experiment and their results
Task: test disks of various sizes at various distances were compared by participant to a comparison disk at a fixed distance
Results: the size of the retinal image changes with viewing distance. Removing distance cues creates a dysfunction in perceptual size constancy as the brain can only use the retinal image
What is Emmert’s Law?
The size of a retinal after-image is fixed
Perceived size of the after-image depends on viewing distance
What are two factors that affect perceived size of a viewed object?
Relative size: comparison to the size of surrounding objects
Shape/object constancy: perceived shape of the object doesn’t change, compared to retinal image
What is constructivism?
A form of empiricism proposed by Ames. Notion that the aim of visual processing is construct an internal model of the outside world, using assumptions to form a percept
What assumption does the brain prioritise when viewing the Ames room illusion?
The brain prioritises the assumption that rooms are typically rectangular over that of constantly sized people, regardless of conscious awareness
Define an absolute threshold
Detecting the presence of a stimulus
Minimum intensity at which the stimulus is ‘just’ detectable
Define a relative threshold
Telling two stimuli apart
What does a psychometric curve plot?
Detectability vs stimulus intensity
Shape of the curve is influenced by noise
What are the two kinds of noise that can influence a psychometric curve?
External noise: variation in the stimulus or the environment that affects performance
Internal: variation in the observer
What are the two kinds of noise that can influence threshold values?
Random noise: the direction of the error varies randomly from trial to trial
Systematic: the direction of the error is constant
What are the outcomes of noise in threshold measurement on the shape of psychometric curve?
Random: curve is more shallow, more variability and less robust data
Systematic: offsets the curve producing the wrong curve
What are the desired properties of a threshold?
Validity: the observer can actually perform the task at threshold level
Reliability: you would get close to the same value if measured again
What are the issues with subjective threshold measures?
Individual variation in threshold detection
No measure of if they can actually see it when they say they can