Sensation and Perception - Chapters 1 & 2

Perceptual Process

Begins with stimuli, ends with perception, recognition, and action

Perception vs Sensation

Perception: higher level brain processes involved in interpreting events and objects

Sensation: detecting elementary properties of a stimulus

Distal Stimulus

The real physical thing in the environment

called distal because it is ‘distant’

principle of transformation

stimuli and responses created by stimuli are transformed, or changed, between the distal stimulus and perception

proximal stimulus

image created on the retina

principle of representation

everything a person perceives is based not on direct contact with stimuli, but on representations of stimuli that are formed on the receptors and the resulting activity in the person’s nervous systems

sensory receptors

cells specialized to respond to environmental energy

visual pigment

light-sensitive chemical found in visual receptors

transduction

the transformation of one form of energy to another (light to electrical for sight)

neural processing

transformation of signals in the brain

primary receiving area

where electrical signals from each sense arrive in the cerebral cortex

cerebral cortex

layer of the brain that creates perceptions and other functions such as language, memory and thinking

occipital lobe

used mostly for vision

temporal lobe

used mostly for hearing

parietal lobe

used for the skin sense; touch, temperature, and pain

frontal lobe

receives signals from all senses, plays an important role in perceptions that involve two or more senses

visual form agnosia

an inability to recognize objects

knowledge

any information that the perceiver brings to a situation

bottom-up processing

perception based off of stimuli reaching the receptors

top-down stimuli

perception based off of knowledge

stimulus-perception relationship

relates stimuli to behavioral responses

stimulus-physiology relationship

stimuli and physiological responses (i.e. brain activity)

method of limits

threshold measurement where the experimenter adjusts the intensity until the subject can no longer detect the stimuli

absolute vs difference threshold

absolute: smallest simulus level that can be detected

difference: smallest change in stimuli where the change can be detected

method of adjustment

the subject adjusts the level of the stimuli

method of contant stimuli

stimuli in a range are presented to the subject in a random order

*most time consuming and accurate test

magnitude estimation

a numeric value is assigned to an intensity level, and the subject is asked to assign a new numeric value to different levels of intensity based off of the first one they were shown

phenomenological report

describing something that you see

What visible light can humans see?

400-700 nanometers (nm)

fovea

center spot on the back of the eye where focused light is directed, contains a much higher concentration of cones than the periphery of the eye

macular degeneration

destruction of the fovea, more common in older people, makes a blind spot in the center of your vision

retinitis pigmentosa

degeneration of the periphery rods, causes ‘tunnel vision’

accomodation

the change in the lens’s shape that occurs when the ciliary muscles at the front of the eye increase the curvature of the lens, to help focus light on the retina

Myopia

When light is focused in front of the retina (near-sightedness)

presbyopia

loss of the ability of the eye to accommodate (old eye)

hyperopia

light focuses behind the retina (farsightedness)

isomerization

when the retinal part of the visual pigment bends and changes its shape

dark adaption

increasing sensitivity to light in the dark

dark adaptation curve

increases rapidly in first 3-4 minutes, than steadily until 20 or 30 minutes. dark-adapted sensitivity is about 100,000x better than light-adapted sensitivity when the darkness began

dark adaptation rods vs cones

cones start out much more sensitive, but by ~5 minutes hit their max and stop increasing sensitivity

rods steadily increase sensitivity throughout and end up more sensitive than cones after ~7 minutes

two important connections between perception and physiology

1. our sensitivity to light depends on the concentration of visual pigment

2. The speed at which our sensitivity increases in the dark depends on the regeneration of the visual pigment

Purkinje shift

We are more sensitive to low wavelength light (blues and greens) during dark adaptation

Changing the stimulus intensity

does not affect the size of the action potentials, but does affect the rate of firing