Sensation & Perception Notes

Basics

Sensation & Perception

• Sensation

  • The stimulation of sensory receptors & transmission of sensory information to the central nervous system (CNS)

• Perception

  • The psychological process by which we interrupt sensory info

• Absolute threshold

  • Weakest amount of stimulus that can be sensed

    • Thresholds vary between individuals & other organisms 

• Difference threshold

  • Minimum amount of difference that can be distinguished between two stimuli

    • Also called just noticeable difference (jnd)

• Signal detection theory

  • Distinguishing sensory stimuli that takes into account the setting 

    • Physical state, mood, & expectations (EX. parents hearing a faint newborn whimper over louder sounds)

• Sensory adaptation

  • Becoming more sensitive to weak stimuli, & less sensitive to unchanging stimuli (EX. Bart’s smelly food)

Vision - The Eye

• Pupil 

  • Opening in eye changes shape based on light & emotions

• Lens

  • Adjusts to the distance of an object by changing it’s thickness

    • Focuses on objects

• Retina

  • Takes focused light & image & acts like the film of a camera

    • Contains photoreceptors which carry the info to the brain via the ontic nerve

• Photoreceptors

  • Neurons in the retina

• Rods & Cones

  • Are photoreceptors

• Rods

  • Allows us to see in B/W

  • Sensitive to only light

• Cones

  • Color vision

• Optic nerve

  • Transmits neural impulses from the eye to the brain

• Blind spot

  • area where optic nerve leaves the eye

    • No photoreceptors in the area

• Visual acuity

  • The sharpness of vision

Color Vision

• Afterimage

  • Visual sensation that occurs after the original stimulus 

  • Complimentary color

• Complimentary

  • Opposite colors (Red/green)

• Color blindness

  • Caused by missing or defective cones

Hearing

• Cochlea

  • Snail shaped structure that produces nerve/sound impulses from vibrations

• Auditory Nerve

  • Bundle of nerves carrying sound from the cholera to the brain

• Conductive deafness

  • Deafness caused by damage to the middle ear

• Sensorineural deafness

  • Deafness caused by damage to the inner ear or auditory nerve 

    • Sounds of certain frequencies are not heard

Smell

Odors are detected by receptor neurons high in each nostril

• Olfactory nerve

  • Transmits odors to the limbic system of the brain

    • Contributes to taste

Taste

• Four basic taste qualities

  • Sweetness, sourness, saltiness, and bitterness 

    • umami= savory meat flavor

• Flavor of food

  • Combination of odor, texture, temperature, and taste

Skin senses

• Touch

  • Combination of pressure, temperature, & pain

  • Some areas of the body are more sensitive

    • More nerve endings

• Pain

  • Gate theory - only a small amount of info can be processed by the nervous system at a time

  • Flooding brain w/ other stimulus blocks some pain messages

Perception

• Gestalt

  • The experience that comes from organizing bits of information into meaningful wholes

• Proximity 

  • We group items together just because of their closeness

• Similarity

  • We think of similar objects as belonging to each other

• Continuity

  • We want to see smooth continuous patterns (lines & waves) not disrupted ones (half-circles)

• Common fate

  • We think things that move together, belong together

• Closure

  • We perceive a complete image even when our senses are missing information

    • Brain fills in the rest

• Figure-ground perception

  • The perception of figures against a background

Motion

• Stroboscopic Motion

  • The perception of movement from rapid progression of images

Depth Perception

Two ways to see depth perception

1. Monocular cues

2. Binocular cues

• Monocular cues

  • Needs only one eye to perceive depth

    • Perspective

    • Clearness

    • Overlapping

    • Shadow

    • Gradient texture

    • Motion parallax

• Binocular cues

  • Retinal disparity

    • Brain compares images from two eyes & computes distance

      • The greater the distance between the two images, the closer the object

  • Convergence

    • Neuromuscular cue

    • 2 eyes move inward for near objects

Perceptual Constancies

Perceiving objects as unchanging even as light & retinal images change (4 types)

- the reason for many visual illusions

• Color constancy

  • Tendency to perceive objects as keeping their color even though different light changes the appearance of their color

• Size constancy

  • Seeing objects as having a constant size, even though the distance from them varies

• Shape constancy

  • Perceiving objects have only one shape, no matter the angle you view it

• Brightness Constancy

  • tendency to see an object equally bright even though when the intensity of light around it changes

• Müller Lyer Illusion

  • Two lines of the same length appear to be of different lengths

    • works because of size constancy

    • doesn’t work in all cultures

    • product of nurture