Chapter 6 Flashcards
object constancy
the brain correctly perceives objects as constant in countless situations despite viewing angles (variation in the physical stimulus)
Variation of visual stimuli emerges from 3 factors:
- viewing position
- illumination
- context
primary visual cortex location
the region of the occipital cortex, where most visual information first arrives
ventral (occipitotemporal) stream function
visual pathway in the brain specialized for object perception and recognition (what), identify what an object is. It focuses on vision for recognition (identification).
dorsal (occipitoparietal) stream function
visual pathway in the brains specialized for spatial perception of objects (where), location of an object. It focuses on vision for action.
superior longitudinal fasciculus location
location of the dorsal stream (where) proceeds to the posterior parietal cortex
inferior longitudinal fasciculus location
location of the ventral stream (what) proceeds to the inferior temporal cortex
Experiments carried out on animals with bilateral lesions of the temporal lobe showed that… stream
…the ventral stream (“what”) was totally disrupted, while
the dorsal stream (“where”) was unaffected
Experiments carried out on animals with bilateral lesions of the parietal lobe showed that… stream
… the dorsal stream (“where”) was totally disrupted, while the ventral stream (“what”) was unaffected
double dissociation
when one perceptual function can be damaged without affecting the other. A classic example of Double Dissociation is speech and language comprehension. Although both processes pertain to use of language, the brain structures that control them work independently.
Do neurons in the ventral stream show object constancy? If yes, explain why and give an example.
Neurons in the ventral stream (“what”) show object constancy. In the brain of someone with a functioning ventral stream, the neurons of the pathway need to be able to recognize the stimuli regardless of its orientation etc. (e.g. hand)
Damage to parietal cortex on right hemisphere
Damage to this area can cause visuo-spatial deficits (e.g., the patient may have difficulty finding their way around new, or even familiar, places)
What is agnosia? What are the kinds of agnosia?
inability to recognize familiar objects or stimuli usually as a result of brain damage (even though the needed organs and memory are not defective)
There are 5 kinds of agnosia: prosopagnosia, category-specific, apperceptive, integrative (subtype of apperceptive agnosia) and associative, which are all connected to the ventral pathway
Visual Agnosia? How it’s caused?
is the failure to recognize objects or identify their uses, which is not due to sensory or memory problems, but the patient is relatively good at perceiving properties such as color, shape, or motion, Patients with visual agnosia can recognize an object when they touch, smell, taste, or hear it, but not when they see it. Visual agnosia is caused due to brain damage along the pathways that connect the occipital lobe of the brain with the parietal or temporal lobe
Auditory Agnosia
inability to recognize sounds
D.F. tasks & visual agnosia
EX: D.F. performed a task, patient with visual agnosia
- could not do the IDENTIFICATION (explicit-matching) task D.F. was given a card and asked simply to orient her hand so that the card would fit into the slot. D.F. failed miserably, for example, orienting the card vertically even when the slot was horizontal - the ventral (what) stream was affected
- could do the ACTION task (where), when asked to insert the card into the slot, however, D.F. quickly reached forward and inserted the card - dorsal stream was fine
Optic Ataxia disorder? Which part of brain affected?
problem with picking up and interacting with objects, but no problem with matching/recognizing the object (e.g. can see a pen in front of them but can’t grab it) opposite of visual agnosia. Optic ataxia is associated with lesions of the dorsal stream (where) in the parietal cortex
Gnostic units (grandmother cells)
Neurons that can recognize a complex object, referring to the idea that the cell (or cells) signals the presence of a known stimulus—an object, a place, or an animal that has been encountered in the past.
Ex: wrong hypothesis: having a chair gnostic unit, an apple gnostic unit etc.
we have feature gnostic unit, shape gnostic unit etc
Ensemble coding theory
recognition is due not to one unit, but to the collective activation of many units (collection of cells). “Granny” is recognized here by the co-occurrence of her wrinkles, face shape, hair color, and so on.
Integrative visual agnosia
can perceive parts of an object, but cannot perceive the “whole”; can’t identify the objects correctly
they can draw some parts of lego
e.g. seeing Lego windows, doors etc. but not the Lego house
Associative visual agnosia?
- can copy objects, but unable to recognize them
- no connection between stored (semantic) knowledge and visual object recognition area, we can’t name it. A patient with associative agnosia can perceive objects with her visual system but cannot understand them or assign meaning to them. At Legoland she may perceive a house and be able to draw a picture of that house, but still be unable to tell that it is a house or describe what a house is for.
Category-specific deficits (agnosia)?
Visual agnosia can be category specific. Category- specific deficits are deficits of object recognition that are restricted to certain classes of objects, which are inanimate and animate (such as cat); sensory motor hypothesis - animate objects share similar features, which is much more difficult to recognize comparing with nonliving objects
single cell recordings
ventral stream cells in the inferior temporal cortex, which demonstrate strong object selectivity. The cells respond to more complex objects, such as hands.
Hierarchical coding hypothesis
-As we move through the ventral stream, each level represents specific features of an object and gets more complex as you go on
Ex: features —> conjunction of features —> component shapes —>object
-explains how we have specific specialized cells that fire in response to specific features of objects.
