psy 405 midterm 1

advantages of electrical potentials

very good temporal

limitations of electrical potentials

very poor spatial

basic color terms

color label that is understood by all speakers and not tied to a particular object

basic components of sensory systems

1. encoding
2. representation
3. decoding

encoding

transducing physical energy into a neural signal

transduction

the conversion of physical energy into neural activity

representation

using populations of neurons to represent information

decoding

reading out the population responses to interpret the info

bayesian inference in perception

1. decode the sensory signals to estimate the stimulus by combing evidence from the sense with prior expectations
2. example of a prior: assume lighting is from above to interpret shading cues

cells are \___ for the information they respond to

selective

cells act as a...

filter or channels for certain information
e.g. different receptors for different wavelengths of light (cones)

center-surround receptive fields are light dart boards

dart (light) in the center earns more positive points (excitation) \n light in the surround earns more negative points (inhibition) \n output of the cells in the total score

cerebral achromatopsia

color blindness due to damage to the cortex

akinestopsia

cortical motion blindness

riddochs syndrome

blind to objects except when they are moving

channels can be measured by

measuring how two stimuli interact
if the stimuli influence each other, they are encoded by the same channel.
e.g. adapting to one side affects the threshold only for similar sizes

clinical evidence for parallel pathways

hemifield neglect (where) and visual agnosia (what)

coding efficiency

making the most of limited resources
brains have limited channel capacity and therefore neurons have a small range of response levels

color blindness affects

mostly males, red and greens

color perception is

universal (which means it may not be as strongly influenced by culture as previously hypothesized)

color vision requires

at least 2 kinds of receptors with different spectral sensitivities

columnar organization

at each location cells in different layers have similar properties, while receptive field change systematically as it moves from one point on the cortex to the next

cones

specialized for good vision at high light levels during the day

cornea and lens

for focusing light to form image on the retina

damage earlier in the visual pathway (eye or early cortex) often results in

general blindness

damage later in the pathway leads to

more specific visual deficits (riddochs and things like that)

dichromat

only have 2 types of cones, more common

different languages apply color terms

to similar regions of the spectrum and show consistent ordering

do responses in the opponent cells give rise to our actual experiences of color

no, the cells we have found in the brain do not predict which hues we see

electrical potentials

examine the brain response to stimuli by measuring the electrical response on scalp (VEP) or surface of the eye (ERG)

evolution of color vision

ancient subsystem (S vs L/M)

modern subsystem (L vs M): modern subsystem is unique to old world primates because they may be specialized for seeing ripe fruits among foliage.

example of redundancy

in language, different parts are often correlated therefore you can remove some of the message and retain the meaning

herman grid

you can see black dots between the squares

simultaneous contrast

where a grey box is behind a white or black background and we overemphasize differences

match bands

where you can see lines between the color band change

developmental plasticity

neural wiring strongly shaped by early experience

perceptual learning plasticity

fine tuning how information is interpreted

adaptive plasticity

sensitivity adjustments to the current environment

compensation plasticity

adjustments for injury or disease or aging

example of predictive coding

represent colors from how they deviate from grey or how faces differ from an average face

stroop effect

color of word has to be identifies but the word spells out a color

mental rotation

rotate an object based off of three separate pictures

visual search

find the different object in a sea of similar ones

fMRI and PET

examining which parts of the brain are active during a perceptual task by monitoring blood flow

fovea

small region of retina specialized for the finest vision, corresponding to the center of gaze

graded potentials

collect information

action potentials

make a decision

hemifield neglect

ignoring one side of the world that resulted from damage at higher visual areas

high threshold means

low sensitivity

how can languages influence some perceptual judgments?

1. some people can be quicker at discriminating names
2. colors if they have diff color names, suggesting weak influence of culture on perception
3. categorical perception (learn categories or sounds specific to our language) and color categories (the world because some colors may look special because they are in the environment)

receptors in the eye transduce a signal

by containing light sensitive photopigments that absorb photons of light

you decide that something is noise or not by

setting criterion (how big the response has to be before you say there is a signal)

primary visual pathway

retina (100 mil receptors) -> optic nerve (1 mill ganglion) -> LGN (2 mill cells) -> striate cortex (600 mil cells)

how must light fall in a receptive field

at a specific point on the retina for the cell to respond
e.g. light falling in the center and surround have opposite effects

hypercolumn

a functional module (1mm square of cortex) that processes all orientations, eye combinations, colors, sizes, motion, and direction for a given location in space

if the response is big, the noise is

low

important insights from introspection

1. color opponency red and green: cells are excited by one color in the center but inhibited in the surround or vice versa
2. lateral inhibition is seen with match bands and when participants are asked to draw the color change they see a line separating the two colors

information bottleneck

theres a limit to the amount of information a system can hold

information processing

reformatting the representations to extract information you want to get

information theory

study of the information in signals and how best to represent it

introspection

thinking about your own perceptual experience

issue with only having one receptor

can't distinguish between change in wavelength and a change in intensity

l and m genes are coded on

the x chromosome

labeled lines

channels are labeled for the information they detect
e.g. stimulus corresponds to the channel with the highest response

languages differ in the

number of color terms

lateral connections and feedback

lots of crosstalk between and within stages

limitations of fMRI

poor temporal resolution and somewhat poor spatial resolution

linking physiology to psychophysics can we explain all contrast effects by retinal processes?

no, things like koffkas ring and shading of an object show how we use our beliefs to shape what we percieve

metamers

lights that are physically different but look the same

monochromats

one receptor type

trichromats

three cone types

multiple channel models

a bank of filters tuned to different levels of the stimulus
e.g. different filters for different positions or colors

nasal fibers

retina crosses over so each LGN represents contralateral visual fields

four parts of a neuron

cell body, dendrites, axon, synapse

cell body

contains most of the machinery to keep cell functioning

dendrite

fibers for receiving information from other neurons

axon

fiber for sending information to other neurons

synapse

where neuron makes contact with other neurons

neurons carry information by

the size and pattern of the response and the pattern of the connections

neuropsychology

study perceptual changes in patients with brain damage

normal trichromats have three cone types

1. L cones for long wavelength
2. M cones for medium wavelengths
3. S cones for short wavelengths (but L and M have similar sensitivities)

off center cell responds best to

a dark spot that just covers the center

on center cell responds best to

bright spot that just covers the center

optic disk and optic nerve

receptor free hold in retina where ganglion cell axons leave the eye (optic nerve)

parallel pathways begin with

different cell types in the retina

parallel processing

different pathways are used to represent different aspects of the world (objects vs motion)

perception is a

guessing game (combining evidence with our beliefs)

perceptual learning example

people get better at seeing things the longer they look

perceptual learning is thought to reflect changes in how we

read out or decode the information in sensory representations

plasticity

representations are strongly shaped by experience

population code

the stimulis are represented by the distribution of activity across the population

predictive coding

encode stimuli by how they deviate from you expectations

primary visual cortex is also known as

striate cortex or V1

principle of univariance

wavelength affects the probability that the photon is absorbed, but once absorbed the response is independent of wavelength

problems with thresholds

1. limited by noise therefore they are not all or none
2. detection depends on sensitivity and criterion
3. uncertainty with threshold judgments in the presence of noise

prosopangnosia

inability to recognize faces

reaction times

measure of the speed of a response

receptive field

area on the retina which a cell responds

receptive fields depend on pattern of

synaptic connections to the cell

receptive fields in the LGN

are center surround and monocular (only receives output from one eye)