PSYC 251 exam 2 - perception

perception

• Experiences resulting from stimulation
of the senses
• The set of processes by which we
recognize, organize, and make sense of
the sensations we receive from
environmental stimuli
• What we sense (in our sensory organs) is
not the same as what we perceive (in
our minds

perception problem

Understand what is going on out there
(outside the brain)

perception importance

Necessary in order to know how to act
to achieve goals

the inverse problem of perception

The inverse problem: how to determine
the distal stimulus from the proximal
stimulus

genes - perception

information
learned on
timescale of
evolution

environmental context - perception

info learned now

proximal stimulus

the stimulus itself

• the energy or matter that impinges on the sensory receptors

distal stimulus

an object or process out in the world

sensory receptors

specialized cells to transduce (convert) external phenomena (light, sound, pressure, etc…) into neural signals

neural pathway

from sensory receptors via thalamic nuclei to cerebral cortex

hierarchy of cortical areas

attemot to construct useful representations of distal stimulus

percept

mental representation of the distal stimulus

transduction

conversion of light into neural signals → retina

photoreceptors

specialized cells for transduction

two types of photoreceptors

rods and cones

1 type of rod, 3 types of cones

cones are concentrated in the _______ and provide greater visual _____

fovea; acuity

primary visual pathway

ganglion cells → LGN (thalamus) → primary visual cortex

visual fields

• both visual fields on both retinas

• partial crossover at optic chiasm

left visual field in

right V1

right visual field in

left V1

sound

changes in air pressure

ear drum (tympanum)

converts changes in air pressure into mechanical vibrations

vibrations travel through _____ of middle ear (ossicles) to oval window of ______

bones, cochlea

cochlea

fluid filled tubes with basiliar membrane

inner ear

pressure waves travel down the cochlear and back out towards the round window

hair cells along the basiliar membrande in cochlea detect…

vibrations

__________ ______ cause hair cells (cilia) to sway

pressure waves

location of maximal excitation along the basilar membrane depends on

sound frequency

where are frequencies located in the organziation of the basialr membrane

• high frequencies near the base

• low frequencies near the apex

primary auditory pathway

Auditory nerve → Cochlear nuclei (medulla) → Superior olivary nucleus (pons) → Nucleus of lateral lemniscus (pons) → Inferior colliculus (midbrain) → Medial geniculate nucleus (thalamus) → Primary auditory cortex

conduction deafness

Damage to outer/middle ear (e.g., ossicles);
Disrupts sound transmission to the cochlea

sensorineural deafness

damage to cochlear hair cells or auditory nerve

primary auditory cortex damage

Often unilateral damage; Impairs sound
localization

higher order auditory cortex damage

- Deficits in understanding speech and melody
• Difficulty interpreting emotional intonation
(e.g., praise vs. sarcasm)

somatosensation types: (4)

• mechanoreception

• thermoreception

• nocioception

• proprioception

mechanoreception

detects pressure, vibration, distortion

thermoreception

detects hot and cold

nocioreception

detects harmful chemical, mehanical or thermal stimuli

proprioception

detects mechanical forces on muscles, tendons and joints

primary somatosensory pathway

dorsal root ganglion → gracile cuneate nuclei (medulla) → ventral posterior nuclei (thalamus) → primary somatosensory cortex

perception inverse problem

Working backwards from what we sense (proximal stimulus) to figure out what's our there in the world (distal stimulus)

sensory adaption

• A decrease in sensitivity of sensory receptors to a constant stimulus

• Allows sensory systems to be less responsive to unchanging stimuli

• The influence of context on perception begins very early in the sensory pathways

The proximal stimulus is represented on a _______ scale, not an
absolute scale.

relative

visual adaption: Ganglion cells adjust ______ ____ to match ambient light

firing rate

visual adaption: response shifts

brighter envirnomental require stronger stimuli to trigger firing

visual adaption function

detect relative brightness, not absolute values

weber’s law

helps understand how people perceive different stimuli.

• The law reveals that perception of stimuli is relative, not absolute.

  • people don't perceive stimuli in terms of their absolute intensity but rather their intensity relative to other stimuli.

auditory adaption

reduced sensitivity to repeated or continuous sounds

Examples:

• Adapting to background noise (e.g., air
conditioner).
• Detecting volume changes in quiet vs.
noisy environments.

weight and webers law

JND in Weight: ~2% of the
object’s weight

• Heavier objects require greater
changes to detect differences.

sound and webers law

• just noticeable difference (JND) of ~5% change in sound intensity,

• for a listener to perceive a difference in loudness, the change in sound intensity must be at least 5% of the original sound's intensity.

somatosensory adaption: SA

slow adapting

somatosensory adaption

RA: rapid adapting

receptive fields

Area of sensory surface to which a neuron responds

higher-order neurons have _____ receptor fields

LARGER

higher-order neurons respond to more ________ sensory stimuli

complex

receptive field of photoreceptors

area on retina

• smaller receptive field for receptors in centre

receptive fields: retinal ganglion cells recieve input from

multiple bipolar and amacrine cells

each successive neuron after photoreceptors recieve input from ______ photoreceptors

multiple

AP of ganglion cell

• At rest, ganglion cell is
  firing at some baseline
  level

• No change when light
  is outside the receptive
  field if our ganglion cell

• Light at centre of
  receptive field =
  increased firing rate

• No change when light
  is outside the receptive
  field if our ganglion cel

• When light is in the
  inhibitory surround,
  ganglion cell responds
  even less

receptive field of a hair cell

freuency of sound

receptive field of a mechanoreceptor

area on skin

receptors on surface of skin

smaller receptive field

receptors deeper in skin

larger receptive field

Somatosensory center-surround receptive fields

lateral inhibition:

• process where activated neurons inhibit the activity of neighboring neurons. This means that when one neuron is stimulated, it can suppress the response of adjacent neurons.

  Purpose: sharpens sensory perception by emphasizing the center of a stimulus while reducing the influence of surrounding stimuli. It allows for better localization of sensory inputs and improves contrast.

topography

spatial organization of sensory information, where the arrangement of sensory receptors on the body or sensory surface is preserved and mapped onto the primary sensory cortex.

cortical magnification

amount of cortical area dedicated to a body part or sensory modality is proportional to the density of sensory receptors in that area.

• Areas of the body with a higher concentration of sensory receptors (e.g., fingertips, lips) are represented by a larger area in the sensory cortex. This allows for more detailed processing of sensory information from these regions.

the small central region of the visual field projects to a large part of

primary visual cortex

visual cortical magnification

disproportionate allocation of cortical area in the brain to processing sensory input from sensitive/ precise areas

plasticity

Changes in neural organization
Occurs from the molecular to the systems level
Synaptic plasticity: Changes in the strength of synapses
Cortical reorganization: Changes in topographic maps

Reorganization of retinotopic map

Lesion of the visual field (in both eyes!) leads to reorganization in primary visual cortex

tinnitus

perception of sound in absence of auditory stimulation

causes of tinnitus

Damage to either cochlea
or structures along auditory pathway or
somatosensory structures or limbic system
or reorganization of tonotopic map

reorganization of tonotopic map

increased spontaneous firing of neurons and changes in
frequency representation → Phantom perception (tinnitus)

reorganization of somatotopic maps and phantom limbs example

Example: After amputation of arm, pursing of lips causes perceived sensation in missing arm

• When a person who has had their arm amputated purses their lips, the sensory stimulation in that area of the face can activate the restructured brain region. Because of the reorganization, this stimulation can lead to the perception of sensations in the missing arm.

• some individuals continue to feel sensations in the area the limb once was: phantom limb sensation

hierarchal organization

lower-order sensory neurons (those closer to sensory receptors) to higher-order neurons (those farther from sensory receptors)

• receptive fields get LARGER

• sensory features more COMPLEX, abstract, MORE SPECIFIC

• multi-sensory integration increases

hierarchical organization, how does processing proceed?

processing proceeds in serial (sequentially), parallel (simultaneously) and is recurrent (loops)

Hierarchy in visual system

V1 (striate cortex) → V2 (extrastriate cortex) → visual association cortex (V3, V4, V5, MST) → Multimodal association (VIP)

cortical columns

• Organization of orientation
feature detectors in columns in
V1
• For each location in visual field,
for each eye, you have a column
of detectors (neurons) tuned to
all orientations
• Organized by eye (ocular
dominance columns) and by
orientation (orientation
columns)

blobs

specialized cells for processing colour

Hierarchy in auditory system

Modularity:
• Primary auditory cortex =
A1 = Core
• Secondary auditory cortex
= A2 = Belt
• Tertiary auditory cortex =
auditory association cortex
= Parabelt (PB), etc...
• Multimodel association
cortex = T2/T3, PP, etc..

auditory: directional feature dectors in _______ ________ __ _____

superios collilculus of ferret

Auditory directional feature detectors - Interaural Time Difference (ITD)

The slight difference in sound
arrival time between the
two ears helps determine
the horizontal location of
a sound source

• used to localize sound horizontally

Auditory directional feature detectors - coincidence detectors

Neurons fire only when signals from both ears arrive simultaneously.

Hierarchy in somatosensory system

Modularity:
• Primary somatosensory
cortex = S1= BA 1, 2, & 3
• Secondary somatosensory
cortex = S2 = PV
• Tertiary somatosensory
cortex = somatosensory
association cortex = BA 5,
MIP, AIP, etc...
• Multimodal association
cortex = VIP, etc...

Somatosensory orientation feature detectors in S2

respond to touch along a specific direction in specific part of skin

Complex somatosensory feature detectors - Motion-sensitive neurons:

respond to any motion in receptive field

Complex somatosensory feature detectors - orientation-sensitive neurons

respond to motion along a particular axis

Complex somatosensory feature detectors - direction sensitive neurons

repsond to motion in a particular direction

visual what and where streams

dorsal pathway - where

ventral pathway - what

visual WHAT stream - ventral pathway

• Face sensitive cells in fusiform face area (FFA) within IT

• Damage to FFA = prosopagnosia (inability to perceive faces)

visual WHERE streams - dorsal pathway

Intraparietal sulcus (IP)
• Anterior (AIP) : Represents space for hand movements
• Medial (MIP): Represents space for arm movements
• Lateral (LIP): Represents space for eye movements
• Ventral (VIP): Represents space for facial movements

AH MA LE VF

Damage to IP = Spatial attention deficits/ neglect

V5 (motion detection) damage

Akinetopsia (motion blindness)

Bottom-up

Stimulus driven
Feedforward connections
Depends on proximal stimulus and genetic “hard-wiring” of sensory systems

Top-down

Driven by goals and expectations
Feedback connections
Depends on past experience, internal state, environmental context

perception depends on bottom-up or top-down influences?

BOTH

top-down likelihood principle

We perceive the world in a way that is “most likely” based on our past experience

Interactive Activation Theory: McClelland and Rumelhar

• model of letter and word perception

• integrates bottom-up and top-down processes

bottom up processing the word CAT example

Feature detectors → features excite or inhibit letters → letters compete with other letters and excite or inhibit words

top down processing CAT example

words compete with other words and excite letters

The right visual field is processed by which retina(s) and which hemisphere(s) of primary visual cortex?

both retinas, left primary visual cortex