Perception and Cognition

Cognition

Mental processes involved in acquiring, processing, and storing information

Environmental stimulus

Physical or chemical energy from the external world that is detected by sensory receptors

definition of motion

change over space and time

stimulation in MT in non primate humans

induce percept of motion

prosopagnosia vs object agnosia

prosopagnosia: inability to recognise face (self included). able to recognise objects

object: inability to recognise different types of objects by vision but can via touch but are able to draw from memory. able to recognise face

Signal detection theory

Quantifies the ability to discriminate between stimuli and measure the amount of information in a stimulus

Retina

Layer at the back of the eye that contains photoreceptors and converts light energy into neural signals

Physical energy

Energy in the form of light or sound

Chemical energy

Energy in the form of taste or smell

Neural signals

Electrical signals generated by sensory receptors and transmitted to the brain

Perceptual experience

Subjective interpretation of sensory information, resulting in conscious awareness

Criterion

Decision threshold used to determine whether a stimulus is present or absent

Sensitivity

Measure of the ability to detect weak stimuli or differences between stimuli

Acuity

Measure of the ability to perceive spatial details or fine differences

Cones

Photoreceptors in the retina that are responsible for color vision and high acuity

Rods

Photoreceptors in the retina that are responsible for low-light vision and peripheral vision

Central vision

Visual field focused on the central part of the retina, providing high acuity

Peripheral vision

Visual field outside the central part of the retina, providing low acuity

Receptive field

Area of the visual field that influences the activity of a neuron

Off-center receptive field

Receptive field where the center inhibits the neuron and the surround excites the neuron

Convergence

Combining inputs from multiple photoreceptors onto a single bipolar cell or ganglion cell

Divergence

Spreading of information from a single input to multiple outputs

Orientation tuning

Preference of a neuron to respond to stimuli with a specific orientation

Motion vision

Ability to perceive and interpret visual motion

MT (Middle Temporal) area

Cortical area strongly implicated in motion perception

Akinetopsia

Motion blindness caused by damage to the MT area

Ventral visual cortex

Cortical area involved in processing visual information related to object recognition and color perception

Colour constancy

Ability to perceive the true color of an object despite changes in illumination

Metamers

Different stimuli that are perceptually indistinguishable

Trichromatic vision

Ability to perceive color using three types of cone photoreceptors

Dichromatic vision

Ability to perceive color using only two types of cone photoreceptors

Cerebral achromatopsia

Complete or partial loss of colour vision despite intact functioning due to damage in the ventral visual cortex —> damage to V4

Surface reflectance

Proportion of each wavelength of light that a surface reflects

Illuminants

Power at each wavelength of light illuminating a scene

Filter

Translucent material that selectively transmits or absorbs certain wavelengths of light

Colour constancy

Ability to perceive the true color of an object despite changes in illumination

Colour perception

Subjective interpretation of the wavelengths of light reflected by objects

Colour blindness

Inability or reduced ability to perceive certain colors

Tetrachromatic vision

Ability to perceive color using four types of cone photoreceptors

Cortical areas

Regions of the brain involved in processing specific types of information

Memory

Mental process of encoding, storing, and retrieving information

Colour perception

Subjective interpretation of the wavelengths of light reflected by objects

Colour constancy

Ability to perceive the true color of an object despite changes in illumination

Colour discrimination

Ability to distinguish between different colors

what are 'hits' in signal detection theory?

correct discrimination of what between stimuli

correct rejection (signal detection theory)

correct rejection of noise in the absence of noise

false alarms (signal detection theory)

no stimulus, but response

miss in signal detection theory?

signal present but subject response is no

criterion in middle?

best possible correct percentage

criterion on left

more chances to make false alarms to minimise misses

criterion on right

more misses. do not want to stop what they are already doing

which scenarios will have lower overall accuracy?

1. criterion in middle

2. criterion on left

3. criterion on right

2. criterion on left

3. criterion on right

what is sensitivity?

being able to discriminate between noise and stimuli, independent of criterion

no sensitivity?

no discrimination, chance

high sensitivity in signal detection theory

distribution almost no overlap. almost perfect discrimination

moderate sensitivity?

moderate overlap

what information do we get if there is response only to the L-cone (long wavelength)?

not much information about intensity but unlikely for the room to be completely dark.

what information do we get if there is response only to the L-cone (long wavelength) & M-cones?

more response in L-cones, light more likely to be reddish

M-cone, light likely to be greenish

if same, yellowish or bluish

what info can we infer if L-cone is more responsive than the M-cone?

the light may have a higher sensitivity, longer wavelength, or lower intensity light that is close to the peak of L-cone sensitivity

cognitive impenetrability give example

even knowing reality you cannot change your perception of a stimuli .

shepherds table illusion: table tops look different proportions if measure, they are same, knowing this you still see disproportion.

perceptual competencies

emerge early in development and show bias towards convex stimuli. seen also in adults

How can we test hearing in newborn babies?

EEG. newborns given headphones, and given bursts of sound to either ear and check expected response in auditory cortex.

emergent properties. give example

where our brain can infer information about stimuli even there is limited sensory information

static point-lighter walker seen as several static dots but once move, they are seem to be human walking

central vs peripheral vision

central - sensitive to changes in high and low spatial frequencies

peripheral - sensitive to low spatial info . lower acuity than central

ocular dominance columns

striped pattern of ocular parts corresponding to light with dark regions for ipsilateral and contralateral input located in V1

how do we lose balance

when visual motion signals are disrupted

what information does form give

depth perception

dimensions of visible colour

colour vision based on 3 cones; RBG

history of trichromatic colour vision

L-cone mutation resulting in M-cone

modular organisation

different visual areas that specifically encode information of a visual scene

the binding problem

integrated visual experience, we experience a very unified and coherent percept

issues with object recognition models

a lot of templates are needed even for simple objects

when there a lot of images together it is hard to process objects

it is hard to recognise unusual positions of a visual scene

we can identify many objects despite having different forms

Q: What's in the inferior temporal cortex

A: ventral stream and large receptive fields

Perception

Process of interpreting sensory information and making sense of the world

Inputs

Sensory information received from the external environment

Outputs

Perceptual experiences or mental representations produced by the brain

Stages of perceptual processing

Environmental stimulus → Sensory receptors → Transduction → Neural activity → Perceptual experience

Transduction

Conversion of physical or chemical energy into neural signals

Black box

Metaphor for the brain, representing the unknown processes that occur between sensory input and perceptual output

Neuroimaging

Techniques used to visualize and study brain activity

what are the main characteristics of perception?

1. emergent properties

2. cognitive impenetrability

3. lack of detail

4. perceptual competencies

what does it mean by lack of detail as one of the main components of perception? give example

we think our perception is detailed when in reality it is not

spot the difference and change blindness.

what is visual angle

amount of retina the object takes up

what is contrast

difference in dark and light

what is spatial frequency? give example:

rate of change over space. being able to see edges in pictures

what is temporal frequency

rate of change over time

True/ False: visual systems most sensitive to things that change slowly than fast

False

what is the order in which light enters the retina?

rods and cones (photoreceptors) to bipolar cells to ganglion cells

what happens in each stage of the retina?

it a competition for resources and pressure for efficiency

what are the layers of the retina?

cones/rods, bipolar cells, ganglion cells

2 photoreceptors

rods and cones

What are rods?

photoreceptors that are highly sensitive but low acuity. they are sensitive to low levels of light. contributes to peripheral vision but no colour vision

what are cones?

photoreceptors that have low sensitivity and high acuity. contribute to colour vision and do not work well in low levels of light

central pathway

photoreceptors receive light info, outputs to bipolar cell layer in the central retinal pathway that correspond to central visual field

what do each cone receptors project to in the central pathway?

2 bipolar cells:

1. on bipolar cells

2. off bipolar cells

When do “on bipolar cells” respond?

when there’s an increase in cone response

off bipolar cells

decrease in cones response

what happens during divergence

increases acuity but less efficient due to more competition of resources

what happens during convergence?

reduce acuity but increase efficiency and sensitivity and receptive field size