Brain and Behavior Quiz 3

optic nerve

goes from the retina to the optic chiasm

optic chiasm

where the left and right optic nerves cross

optic track

goes from the optic chiasm to the lateral geniculate nuclei (LGN)

optic radiation

goes from the LGN to the primary visual cortex

lateral geniculate nuclei (LGN)

an important structure for the relay of visual information

location of the LGN

the thalamus

nuclei in the thalamus

also very densely packed

division of information from the eyes to the hemispheres

in humans, ½ of the info from each eye/retina goes to the contralateral hemisphere and the other ½ of the info from each eye/retina goes to the ipsilateral hemisphere

the nasal half of each eye/retina

the half closer to the midline/nose

the temporal half of each eye/retina

the half closer to the sides of our heads/ears

visual info traveling from the nasal half of the eye/retina

the nasal half of the info from each eye goes to the contralateral hemisphere

visual info traveling from the temporal half of the eye/retina

the temporal half of the info from each eye goes to the ipsilateral hemisphere

intensive processing of visual info

relayed from the thalamus for this process to occur in the occipital lobe

pathways of visual info

not just eyes to thalamus to visual cortex; it's more complex and includes some info moving from the visual cortex forward

area V1

an important point for visual processing that has many neurons, including feature detector neurons

features

the parts or characteristics of some distal stimulus

feature detectors

neurons in V1 that are specialized to detect specific features in the visual field

3 different kinds of feature detectors in V1

simple cells, complex cells, and end-stopped (hypercomplex) cells

simple cells (as a kind of feature detector)

cells that have evolved to typically respond to fixed lines, bars, or edges

complex cells (as a kind of feature detector)

cells that have evolved to typically respond to movement in a specific direction of lines, bars, or edges

end-stopped/hypercomplex cells (as a kind of feature detector)

cells that have evolved to typically respond to movement of line segments toward a fixed boundary

crossing the boundary of end-stopped/hypercomplex cells

if the line segment goes past the boundary, the cell doesn't respond

4 examples of complexity in the visual system

saccades, binocular fusion, processing of visual information that continues beyond V1, and the percept is a reconstructed version of the distal stimulus

1st example of complexity in visual processing

saccades, which are short darting/jumping motions of the eye

stochastic aspect of saccades

it is a stochastic/random process of where our eyes land when we first look at something

discontinuity of saccades and our perception of our vision

these saccades exist in the visual system, but we perceive our vision as a static and smooth process

the theory behind the discontinuity of our perception of vision and what actually occurs in the visual system

the visual system shuts off during these saccades to make it seem more continuous

2nd example of complexity in visual processing

binocular fusion, which is the computationally complex process of combining the separate images perceived by each eye/retina

proximal and distal stimuli in binocular fusion

a single distal stimulus creates 2 proximal stimuli, one in each eye (each being viewed from a different angle)

the retinas' perception of images

each retina forms its own (inverted) slightly offset image

retinas' perception of distal stimuli

each distal stimulus is really 2 distal stimuli: one in each retina

where binocular fusion likely happens

likely mainly occurs in V1

what binocular fusion illustrates

unconscious processing in the visual system

3rd example of complexity in visual processing

processing of visual information that continues beyond V1

post visual-cortex pathways

pathways that move visual information forward from the visual cortex (lots of critical processing happens after info hits the visual cortex)

dorsal stream

the post visual-cortex pathway at the top of the brain that analyzes spatial location and is responsible for visuomotor processing

visuomotor processing

coordinating motor actions with spatial locations

consciousness of the dorsal stream

mostly unconscious

ventral stream

the post visual-cortex pathway at the bottom of the brain that analyzes what things are (meaning)

consciousness of the ventral stream

mostly conscious

2 ways lesions can occur in the dorsal and ventral pathways

they can be created surgically (in animals) or they can occur after a stroke

lesions in the dorsal stream

produce visual ataxia but don't impair the ability to identify objects

visual ataxia

inability to coordinate motor movement with what one sees in space (e.g. not being able to put your foot on a chair)

lesions in the ventral stream

impair identification, but not grasping

lesions in the ventral stream and oral identification

people can still recognize what something is when it is a word spoken to them, but they can't look at something and know what it is

blindsight

when lesions in V1 produce partial (½ of the visual field) or full blindness (phenomenological awareness), but the person maintains some level of spatial awareness

phenomenological awareness

blindness?

how blindsight likely occurs

if the lesion doesn't impact the dorsal stream and some amount of information can get past the lesion in V1 to get to the dorsal stream, that info can be enough to somewhat guide a person's knowledge of where something is in space

4th example of complexity in visual processing

the percept is a reconstructed version of the distal stimulus

change blindness

our inability to recognize changes occurring outside the focus of our visual attention

"spotlight" of attention

to deeply analyze all info in visual space would require too many resources, so we cast a "spotlight" of attention that gets the highest level of processing in order to minimize the compute and resources needed

our assumption of our visual processing

we assume that we process everything in our field of vision to the same high degree, but we don't

the context of a percept

a percept is a reconstruction based on context; the context in which a distal stimulus is situated has a massive influence on the percept that we construct