Psychology Notes on Sensation and Perception

Chapter 5

Sensation (a stimulus-detection process by responding to and translating stimuli into nerve impulses by sense organs)

perception (an active process of organizing stimulus input and giving it meaning) (influenced by the context)

psychophysics: physical stimuli --- psychological experience

1. The process from sensation to perception

• Stimulus is received by sensory receptors
• Receptors translate stimulus properties into nerve impulses(transduction)
• Feature detectors break down and analyze stimulus features
• Stimulus features are reconstructed into neural representation
• Neural representation is compared with previously stored information in brain
• Matching results in recognition and interpretation

1. Synaesthesia (mixing of the senses) theories

• The pruning of neural connections that occurs in infancy has not occurred in people with synaesthesia.
• There is a deficit in neural inhibitory processes that keep input from one sensory modality from overflowing into other sensory areas.

1. Two concerns of psychophysics

• The absolute limits of sensitivity (smallest)
• Sensitivity has to do with the differences between stimuli (difference)

1. The absolute threshold (the lowest intensity at which a stimulus can be detected correctly 50% of time)
2. Decision criteria (a standard of how certain they must be that a stimulus is present before they will say they detect it)
3. Signal detection theory (concerned with the factors that influence judgements)

• Experience
• Participant’s characteristics (conservative or bold)
• Situation’s characteristics (the increasing reward for hits and costs for miss results)

1. The difference threshold (the smallest difference between two stimuli that people can perceive 50% of time)
2. Weber’s law (weber’s fraction- the smaller the fraction, the great the sensitivity to differences) (audition- smallest- most sensitive; taste—largest, least sensitive)
3. Sensory adaptation (sensory neurons respond to a constant stimulus by decreasing their activity and the diminishing sensitivity to an unchanging stimulus) (sensitivity to changes is important to well-being and survival)

10.Subliminal stimuli: stimuli that register on our NS but below our sensory threshold. – little effect on behavior, small effect on attitudes.

The sensory systems

• Vision (700-red to 400-blue-violet)

1. Cornea (a transparent protective structure in front of the eye)

=Light through the eye

1. Pupil (an adjustable opening behind the cornea)

=dilate or constrict to control the amount of light that enters the eye

=low light – dilate-  to improve optical clarity

1. Iris (surrounds the pupil)

=control the size of the pupil

1. Lens (an elastic structure behind the pupil)

=become thinner to focus on distant objects

1. Retina (a multi-layered tissue at the rear of the fluid-filled eyeball)

=myopia(nearsightedness):  the eyeball is longer

=hyperopia(farsightedness): the lens is too thin that the image focuses on a point behind the retina (aging problem that myopia will improve their vision)

= astigmatism: refractive errors due to a curvature of the cornea

1. The rods

=functions best in dim light—black-and-white brightness receptors

=more sensitive to light than the cones

=they can combine their individual electrical messages where the additive effect of many signals enough to fire it

                     =more prevalent on peripheral visual field

1. The cones

=functions best in bright illumination (pigeon & chipmunk poor night vision)

= color receptor

      = more prevalent in fovea 

= Visual acuity 敏感度

        greatest when projects onto the fovea

1. Fovea (no rods)

=contain only cones

=cones each have their own private line to a single bipolar cell

rods and cones send messages to the brain via

• Bipolar cells & ganglion cells
• (bipolar cells – ganglion cells –form-- optic nerve)

1. optic nerve—formed by the axons of the ganglion cells

=blind spot

1. Photopigment (a protein molecule)-visual transduction

=the absorption of light by it produces a chemical reaction that changes the rate of neurotransmitters release at the receptor’s synapse.

=the greater the change the release, the stronger the signal passed on to the bipolar cell and to the ganglion cells

=nerve responses are triggered at rod or cones, bipolar cell and ganglion cell, the message is—visual relay station in the thalamus—the visual cortex of the brain.

1. Brightness vision

=rods have much greater brightness sensitivity than cones except at the red end

=cones are more sensitive to low illumination in the greenish-yellow—change the color of fire engine in order to increase visibility to both rods and cones in dim lighting

=rods sometimes not ready to fulfill their function-theatre

1. Dark adaptation (the progressive improvement in brightness sensitivity that occurs overtime under low illumination)

=when absorbing light, photopigment is deleting

=during dark adaptation, the photopigment molecules are regenerated and sensitivity increases

=solders wear red lenses because red light only stimulates the cones, so the rods remain in a state of dark adaptation

1. Color vision

1. The trichromatic theory (three types of color receptors (blue, green, red) in the retina) (Van Helmholtz) (high in G & R – longest, but low in B)

=based on the extent to which they are activated by the light energy’s wavelength, receptor send messages to the brain

=if all three cones are equally activated, white! (additive color mixture)

=problem: afterimage and color blindness

1. Opponent-process theory (each of the three cone types respond to two different wavelengths (black or white, red or green, blue or yellow) (Ewald Hering)

=a red-green cone responds with one chemical reaction to a green stimulus and with its other chemical reaction (opponent process) to a red stimulus

= do not occur at the level of the cone

=occur at the ganglion cells

1. Dual-process theory (win-win verdict)

=cones contain one of three photopigments that blue, red and green

=neurons respond in an opponent-process by altering their rate of firing (red light -- cell fire at a high rate; green--low rate)

1. Color-deficient vision

=trichromat (people with normal color vision)

=dichromat (color-blind with one of the system)

=monochromat (sensitive only to black-and-white)

1. Feature detectors and visual association cortex

= feature detectors : fire selectively in response to stimuli that have specific characteristics (new findings that not only to it, but to complex stimuli that through experience)

=visual stimuli are analyzed by feature detectors in the primary visual cortex (occipital lobe), and the stimulus elements are reconstructed and interpreted in terms of input from the visual association cortex

• Point-to-point correspondence –regions of retina & groups of neurons in the visual cortex (except for fovea – large area in the visual cortex)
• Parallel processing:
• Age 10 – cataract

• Audition

1. Two characteristics: frequency and amplitude

=Frequency(pitch): the number of sound waves or cycles per second

=amplitude(loudness): the vertical size of the sounds

1. Auditory transduction

—Strike eardrum (tympanic membrane鼓膜) (a movable membrane that vibrates in response to the sound)

—middle ear with three tiny bones-hammer, anvil, stirrup (amplify the sound waves)

—pressure created at oval window (a membrane forms the boundary between the middle ear and inner ear) by hammer and anvil

—stirrup set the fluid inside the cochlea

—vibrate the basilar membrane, causing a bending of the hair cells in the organ of Corti (contains hair cells that are actual sound receptors)