Lecture 16 Flashcards
Discounts the Illuminant
Estimating the light source and adjusting our perception to maintain stable colours
Colour Constancy
Even when lighting conditions change (e.g. sunlight vs. indoor lighting) we perceive objects as having the same colour
-Allows us to discount the influence of the illuminant and focus on the true colours of objects
Spatiotemporal Event
Motion is…
-A change in position over time
visually-guided actions and interaction with the environment
Motion is essential for…
objects from their background
-E.g. camouflaged animals
Motion helps distinguish…
Akinetopsia
A rare neuropsychological disorder in which the affected individual has no perception of motion
-see life as successive images
-cannot poor themselves water
-cannot detect speed of cars
-dangerous for patients to move around themselves
-can be caused by lesion of areas MT/MST
Apparent Motion
The illusory impression of smooth motion resulting from the rapid alternation of objects that appear in dfferent locations in rapid succession
-E.g. our brain can connect 2 images even though we just have 2 static images
Apparent Motion Illusion
-Fast: probable that this object is going from left to right
-Slow: object just popping up and disappearing
-Different effect when dots are further apart
Motion Detection Circuit (‘‘Reichardt detectors’’)
- M neuron registers a change in position between A and B. But…
-would also respond to 2 still cars
-would also respond to a car moving backwards - Solution : add neuron D which incorporates delay
-perceive orientation
Movement After-Effect
A powerful illusion of motion in the visual image caused by prior exposure to motion in the opposite direction
Aperture Problem
The fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of an object may be ambiguous
Correspondance Problem
The problem faced by the motion detection system of knowing which feature in frame 2 corresponds to which feature in frame 1
Movement Perception
-Motion information from several local apertures (or receptive fields) can be combined to determine the global motion of the object
-There are several directions of motion within each aperture that are compatible with the stimulation the receptor is receiving
-Whichever possible motion direction is the same in all apertures is the true global motion direction of the object
Smooth Pursuit
Voluntary eye movement in which the eyes move smoothly to follow a moving object
Saccade
A type of eye movement, made both voluntarily and involuntarily, in which the eyes rapidly change fixation from one object or location to another (3-4 times every second)
Vergence
A type of eye movement, both voluntary and involuntary, in which the two eyes move in opposite directions
Reflexive Eye Movements
Automatic and involuntary eye movements
-E.g. when the eyes move to compensate for head an body movement while maintaining fixation on a particular target
Microsaccade
An involuntary small jerklike eye movement
-prevent visual fading
-allowing us to see behind the blood vessels in our eye
-improve visibility of sharp details
-compensate for the sudden loss of acuity a few minutes outside the fovea
Saccadic Suppression
The temporary reduction of visual sensitivity that occurs during rapid eye movements (saccades) to prevent motion blur and maintain visual stability
Visual Fading
Effect in which entire photographs of scenes fade to a uniform luminance and hue during normal visual fixation
-visual system forgets that there’s colour present
