Lecture 5: Perception Mechanisms (Vision only) Flashcards
does not produce an accurate internal copy of the external world
vsiual system
eyes are “tricked” into seeing things the way they aren’t; regarded as minor imperfections to one’s vision
visual illusions
Electromagnetic radiation that can be perceived by the human eye (visible light spectrum)
light
light is sometimes defined as waves of electromagnetic energy between ______
380-760 nm
if there is no light, there is no _____
vision
2 notable properties of light
- wavelength
- intensity
plays an important role in the perception of color
wavelength
plays an important role in the perception of brightness
intensity
The amount of light reaching the retinas is regulated by the ____
iris
donut-shaped bands of contractile tissue
iris
the hole in the iris
pupil
light enters through the _____
pupil
Adjustment of pupil size in response to changes in illumination represents a compromise between
- sensitivity
- acuity
ability to detect the presence of dimly lit objects
sensitivity
ability to see the details of objects
acuity
happens during high level of illumination
constriction of pupils
happens during too low level of illumination to activate the receptors
dilation of pupils
Focuses incoming light on the retina
lens
When gaze is directed at something near, the lens assumes its
natural cylindrical shape
On a distant object, the lens is
flattened
process of adjusting the configuration of the lenses to bring images into focus on the retina
accomodation
the difference in the position of the same image on the two retinas
binocular disparity
functions of the retina
- Converts light to neural signals
- Conduct them towards the CNS
- Participates in the processing of the signals
5 types of neurons in the retina
- receptors
- horizontal cells
- bipolar cells
- amacrine cells
- retinal ganglon cells
Specialized for lateral communication
amacrine cells and horizontal cells
retinal neurons communicate both ____ and ____
chemically (synapses) and electrically (gap junctions)
2 visual problems of inside-out arrangement
- incoming light is distorted
- there must be a gap (blind spot) in the receptor layer
- Specialized for high-acuity vision
- Central point of the retina
- Has no rods; only cones
fovea
2 types of receptors in human retina
- cones
- rods
- Cone-shaped receptors
- Specialized in detecting fine details and colors
- Operates best in bright light
- Located around the fovea
cones
- Rod-shaped receptors
- Specialized in detecting black, white, and gray colors
- Do not provide a lot of detail; but allows us to see in dim light
- Located around the edges of the retina
rods
theory that cones and rods mediate different kinds of vision
duplexity theory of vision
duplexity theory of vision
- phototopic vision
- scotopic vision
cone-mediated vision that predominates in good lighting and provides high-acuity colored perceptions
photopic vision
rod-mediated vision that predominates in dim illumination and lacks both the detail and the color of photopic vision
scotopic vision
Graph of the relative brightness of lights of the same intensity presented at different wavelengths
spectral sensitivity curve
2 spectral sensitivity curves
- photopic spectral sensitivity curve
- scotopic spectral sensitivity curve
(spectral sensitivity curve) determined by having subjects judge the relative brightness of different wavelengths of light shone on the fovea
photopic spectral sensitivity curve
(spectral sensitivity curve) determined by asking subjects to judge the relative brightness of different wavelengths of light shone on the periphery of the retina
scotopic spectral sensitivity curve
Visual system is maximally sensitive to wavelengths of about 560 nm
under photopic conditions
Visual system is maximally sensitive to wavelengths of about 500 nanometers
under scotopic conditions
Visual effect of relative brightness observed during the transition from photopic to scotopic vision
purkinje effect
entire area you can see at a particular moment
visual field
explains why the world does not vanish momentarily each time we blink
temporal integration
3 kinds of involuntary fixational eye movements
- tremor
- drifts
- saccades
enable us to see during fixation by keeping the images moving on the retina
eye movements
when eye movements are _____ visual objects begin to fade and disappear
blocked
if retinal images are ______ the images start to disappear and reappear
artificially stabilized
conversion of light to neural signals by the visual receptors
visual transduction
any substance that absorbs light
pigment
A G-protein-coupled receptor that responds to light rather than to neurotransmitter molecules
rhodopsin
Conducts signals from each retina to the primary visual cortex (aka. striate cortex or V1) via the (thalamic) lateral geniculate nuclei
retina-geniculate-striate system
2 parallel channels of communication
- parvocellular layers (P layers)
- magnocellular layers (M layers)
- Runs through the top 4 layers
- Majority of input comes from cones
parvocellular layers (P layers)
- Runs through bottom 2 layers
- Majority of input comes from rods
magnocellular layers (M layers)
parvocellular layers have ___ cell bodies while magnocellular layers have _____ cell bodies
- small
- large
The most informative features of any visual display because they define the extent and position of the various objects in it
edges
nonexistent stripes of brightness and darkness running adjacent to the edges
mach bands
mach bands enhances the _____ at each edge
contrast
area of the visual field within which it is possible for a visual stimulus to influence the firing of a neuron
receptive field
characteristics of some binocular cells
- ocular dominance
- retinal disparity
Respond more robustly to stimulation of one eye than they do to the same stimulation of the other
ocular dominance
Fire best when the preferred stimulus is presented to both eyes simultaneously but in slightly different positions on the 2 retinas
retinal disparity
influences on a visual neuron’s activity that are caused by stimuli outside the neuron’s recep. field
contextual influences
One of the most obvious qualities of the human visual experience
colors
black =
absence of light
produced by the intense mixture of a wide range of wavelengths in roughly equal proportions
white
the perception of an object’s color depends on the ____ that it reflects into the eye
wavelengths of light
theories of color vision
- component theory
- opponent-process theory
- color constancy and the retinex theory
There are three diff. kinds of color receptors (cones), each with a different spectral sensitivity
component theory (trichromatic theory)
Each of the three classes of cells encoded two complementary color perceptions
opponent-process theory
2 diff classes of cells in the visual system
- for encoding color
- for encoding brightness
pairs of colors that produce white or gray when combined in equal measure
complementary colors
Tendency of an object to stay the same color despite major changes in the wavelength of light that it reflects
color constancy
Color of an object is determined by its reflectance
retinex theory
proportion of light of diff. Wavelengths that a surface reflects
reflectance
3 classes of visual cortex
- primary visual cortex
- secondary visual cortex
- visual association cortex
Receives most of its input from the visual relay nuclei (lateral geniculate nuclei) in the thalamus
primary visual cortex
Receive input from areas of the secondary visual cortex as well as the secondary areas of other sensory systems
visual association cortex
Receive most of their input from the V1
secondary visual cortex
2 possible damages to primary visual cortex
- scotoma
- blindsight
Area of blindness in the corresponding area of the contralateral visual field of both eyes
scotoma
having a scotoma covering half of the visual field
hemianopsic
Ability to respond to visual stimuli in a scotoma with no conscious awareness of them
blindsight
most likely to survive damage to primary visual cortex
perception of motion
Most neurons respond most robustly to spatial stimuli
dorsal stream
Most neurons respond to characteristics such as color and shape
ventral stream
failure of recognition that is not attributable to a sensory deficit or to verbal or intellectual impairment
visual agnosias
2 visual agnosias
- prosopagnosia
- akinetopsia
Problems with recognizing whose face they are looking at
prosopagnosia
types of prosopagnosia based on acquisition
- development prosopagnosia
- acquired prosopagnosia
[prosopagnosia] acquired during development
development prosopagnosia
[prosopagnosia] resulted from brain injury
acquired prosopagnosia
Implicated in face identification because parts of it are selectively activated by human faces
fusiform face area
Reversible inactivation of the OFA selectively disrupts the ability to discriminate between faces
occipital face area
Deficiency in the ability to see movement progress in a normal smooth fashion
akinetopsia
akinetopsia can be a:
- permanent result of brain damage
- transient result of taking high doses of certain antidepressants
