wk1: ND - Object Perception Flashcards
Outline the ventral pathway for transmission of information (4)
V1–> V2 –> V4 –> Infero-temporal cortex
Outline the dorsal pathway for transmission of information (4)
V1 –> V2 –> DM/V6 (dorsomedial area) –> posterior parietal cortex
In a word or 2, explain the Ventral and Dorsal pathways (2)
Ventral: “What” pathway
Dorsal: “Where” pathway/”How” pathway
Which visual pathway stream is involved in object perception? (1)
Ventral stream
Can the retina alone distinguish faces?
No. You need your visual system to combine many inputs/responses to do so
Before distinguishing objects such as faces, what must the visual system first do? (1)
Interpret global shape
What feature of V1 allows objects close together to be perceived more easily? Explain
Long-range interaction between neurons. This means that when you have a target in the centre of 2 other targets, the central target can be more easily seen than it would otherwise thanks to this interaction
How does the background relate to an object’s contrast? (1)
Apparent object contrast depends on background: object contrast will appear lower when on a background of higher contrast (this is known as surround suppression) and vice versa
How does V1 fare with contours?
V1 has contour integration, which means contours stick out and are more noticeable
What is the tilt illusion?
Central circular grating with vertical lines and a larger circular grating around it with diagonal lines. Due to the response of orientation-selective cells to the larger circle, the lines in the inner circle appear tilted rather than vertical
What info is fed forward from V1? (3)
Discrete orientation information
Linked borders/contours
Some boundary and edge information
Does V1/primary visual cortex tell you what an object is?
No. It only tell you that an object is present
What are V2 neurons sensitive to? (3)
V2 neurons are sensitive to orientation, colour, and continue the processing of contours
Can V2 respond to illusory contours? What are illusory contours?
yes. Illusory contours are things like fake implied edges such as when you have 2 triangles combined and the edge is implied by pac-man at the vertices
What is V4 responsible for?
Integration of local cues into global shape percepts
How do we know which parts of the brain are involved in object perception? (2)
Lesions
Functional MRIs
In most people, what percentage of coherence is needed to identify a shape?
At least 25%
Is texture important to help us recognise overall global form?
yes
What type of orientation is V4 more sensitive to?
radial and concentric
Define Visual Agnosia
inability to recognise visually presented objects
How can visual agnosia occur?
Through damage somewhere along the ventral pathway
Define Aperceptive agnosia
can’t integrate the component visual features into a global whole
Define Associative agnosia
can’t identify the object with the required knowledge of it (may be able to copy it but doesn’t recognise what it is)
Define Prosopagnosia
“face blindness”, ability to recognise faces is impaired, but other object perception and cognition is intact
