sensation and perception exam 1

Neuron

Electrically excitable cell that processes and transmits information; core building block of the nervous system

Resting potential

The voltage inside a neuron (-70mV) relative to outside when the cell is not being stimulated

Depolarization

Sodium (Na+) flows into the cell, making the inside more positive

Repolarization

Potassium (K+) flows out of the cell, bringing voltage back down after depolarization

Hyperpolarization

Voltage drops below resting potential before returning to baseline

Action potential

All-or-none electrical signal that fires once a neuron reaches critical threshold (~-45mV)

Refractory period

Brief period after an action potential during which another cannot occur

All-or-none principle

An action potential either fires completely or not at all — no partial firing

Synaptic vesicles

Structures that release neurotransmitters into the synapse after an action potential travels down the axon

Photoreceptors

Rods and cones; the only retinal cells directly sensitive to light

Photoisomerization

Process by which light is converted into a neural impulse via photopigment molecules

Pigment epithelium

Layer behind the retina that supplies blood/nutrients to photoreceptors and enables photopigment regeneration

Bipolar cells

Retinal cells that relay signals from photoreceptors to ganglion cells

Ganglion cells

Retinal cells whose axons form the optic nerve

Horizontal cells

Retinal cells that mediate lateral interactions between photoreceptors

Amacrine cells

Retinal cells that mediate lateral interactions between bipolar and ganglion cells

Blind spot

Area with no photoreceptors where the optic nerve exits the eye

Rods

Photoreceptors for dim light/night vision; ~100 million per eye; absent from fovea

Cones

Photoreceptors for color/daylight vision; ~5 million per eye; densest at fovea

Fovea

Retinal region with only cones, responsible for sharp central vision

Dark adaptation

Gradual increase in visual sensitivity in low light as rods take over from cones

Purkinje shift

Shift in peak sensitivity from cones (long wavelengths) to rods (short wavelengths) during dark adaptation

Spatial summation

Multiple rods converging onto a single ganglion cell, increasing sensitivity but reducing acuity

Visual acuity

Ability to see fine detail, best supported by cones in the fovea

Receptive field

Area of sensory surface that, when stimulated, changes a neuron's activity

Center-surround organization

Receptive field structure where center and surrounding area have opposing effects (excitatory/inhibitory)

Simple cells

V1 cortical cells with on/off areas responding best to bars of light at specific orientations

Complex cells

Cortical cells responding to light/dark stimuli and edges regardless of exact location in receptive field

End-stopped cells

Complex cells sensitive to the length of a stimulus

Feature detectors

Specialized neurons/cell groups that respond only to specific stimulus features (orientation, motion, color)

Lateral geniculate nucleus (LGN)

Thalamic relay structure with 6 layers that processes visual input before it reaches the cortex

Magnocellular layers

LGN layers 1-2; involved in detecting movement and flicker

Parvocellular layers

LGN layers 3-6; involved in color and form perception

Retinotopic mapping

Organization where location of neural activity corresponds to location of stimulus on the retina

Cortical magnification

Disproportionately large area of visual cortex devoted to processing foveal input

Orientation columns

Groups of V1 neurons organized by their preferred stimulus orientation

Lateral inhibition

Neural circuit where stimulated neurons reduce activity of neighboring neurons, sharpening contrast

Simultaneous contrast

Illusion where surrounding background affects perceived brightness of a central region via lateral inhibition

Hermann grid illusion

Illusion of gray blobs at intersections of white lines on a black grid, caused by lateral inhibition

Mach bands

Illusory bright/dark bands at edges of a gradient, caused by lateral inhibition enhancing contrast

Dorsal stream

"Where/how" visual pathway to parietal cortex; involved in motion, location, and action

Ventral stream

"What" visual pathway to inferotemporal cortex; involved in object identification, form, and color

MT (medial temporal area)

Brain area with neurons tuned to motion and direction

V4

Visual area involved in color and curved-edge/form processing

Inferotemporal cortex (IT)

Area where neurons respond to complex shapes; final stage of ventral "what" pathway

Fusiform face area (FFA)

Brain region specialized for face recognition

Extrastriate body area (EBA)

Brain region specialized for recognizing body parts

Parahippocampal place area (PPA)

Brain region specialized for recognizing places/scenes

Binding problem

The challenge of how the brain integrates separate features (color, shape, motion) into one perception

Population coding

Using activity across multiple neurons (rather than one) to represent a stimulus unambiguously

Single cell recording

Research method recording electrical activity of individual neurons, typically in animals

PET (Positron Emission Tomography)

Brain imaging measuring blood flow; poor spatial and temporal resolution, involves radioactivity

fMRI (functional MRI)

Brain imaging measuring blood oxygen levels; good spatial resolution (voxels)

Voxel

3D pixel used in fMRI, representing about 100,000 neurons

Diffuse Optical Tomography (DOT)

Portable brain imaging method measuring blood oxygen via reflected light

Psychophysics

Study of the relationship between physical stimulus intensity and perceptual experience

Absolute threshold

Minimum stimulus intensity needed to detect a sensation

Difference threshold (JND)

Smallest detectable difference between two stimuli; just noticeable difference

Method of limits

Threshold method presenting ascending/descending stimulus series to find point of response change

Method of adjustment

Threshold method where subject/experimenter continuously adjusts stimulus intensity

Method of constant stimuli

Threshold method presenting a fixed set of intensities in random order across many trials

Staircase method

Efficient threshold method that reverses direction of intensity change based on responses

Point of subjective equality (PSE)

Stimulus intensity judged equal to the standard 50% of the time

Point of objective equality (POE)

The actual physical value of the standard stimulus

Size-weight illusion

Illusion where the larger of two equal-weight objects feels lighter

Weber's Law

JND is a constant proportion of stimulus intensity (JND = k × I)

Fechner's Law

Perceived intensity increases as a slower (logarithmic) function of physical intensity

Stevens' Law

Power function describing relationship between physical stimulus magnitude and perceived intensity, more broadly accurate than Fechner's Law

Magnitude estimation

Method where subjects assign numbers to stimuli relative to a standard, used in Stevens' Law

Signal detection theory

Framework for measuring sensitivity to a stimulus independent of response bias

ROC curve

Receiver Operating Characteristic curve; plots hit rate vs. false alarm rate to assess sensitivity

Hit rate

Proportion of correct detections of a signal

False alarm rate

Proportion of times a signal is reported when none was present

stevens’ power law

isosensitivity curve

dendrites

a

nucleus

b

cell body

c

myelin sheath

d

axon

e

axon terminals

f

cornea

1

iris

2

lens

3

sclera

4

retina

5

fovea

7

blind spot

8

optic nerve

9

ciliary muscle

12

parasol RGCs

retinal ganglion cells that form the basis of the dorsal (where/how) pathway

midget RGCs

retinal ganglion cells that form the basis of the ventral (what) pathway

MT (medical temporal area)

dorsal stream area with neurons tuned to motion direction and speed; tested using stimuli with dots moving randomly vs coherently

pariteal cortex

dorsal stream endpoint; processes “where” information —> direction and location

V4

ventral stream area with neurons selective for wavelength (color) and form, especially curved edges

ventral stream damage effect

patients cannot identify objects but can still draw them from memory, showing ventral stream is specific to object identification, not general vision

slot task

task used to test dissociation between perceiving an objects orientation (ventral) and acting to insert a card into it (dorsal)

dissociation between perception and action

finding that a persons verbal judgement (ventral) and their hand’s motor response (dorsal) can rely on different, sometime conflicting, info

ebbinghaus-type size illusion (disk experiment)

experiment showing that even when two disks are perceived as equal size (ventral), the hand’s grip size scales to their true size when reaching (dorsal)

binding problem

the challenge of how the brain combines separate neural info about color, shape, and motion into one unified perception