PSYC 1010 Study Guide - Circadian Rhythm, Depth Perception, Sound

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Published on 20 Mar 2013
Chapter 5
Synesthesia = mixed senses condition
Transduction = sensory receptors translate stimuli into nerve impulses
Feature detectors = neurons that break down and analyze the specific features of the stimuli.
- Reconstructed into neural representation using previous stored data
- Ppl w/ synesthesia have "cross wiring" in their brain, evoking responses in another part of the brain
dedicated to another sensory modality.
-One theory as to the sensory mixing is that the pruning of neural connections that occurs in infancy has not
occured in people with syn
-Another theory is that w/ syn, theres a deficit in neural inhibitory processes in the brain that ordinarily keep
input from one sensory modality from "overwhelming' into other areas. Both normal perceptual processes
and synesthesia relate in neuroscience called the binding problem.
Sensation = stimulus-detection process by which our sense organs respond to and translate environmental
stimuli into nerve impulses that are sent to the brain.
Perception = making "sense" of what our senses tell us, organizing stimuli and giving them meaning.
- Different animals are more sensitive 2 particular stimuli from adaption 2 environment (IE carrier
pigeons/magnetic field and Sharks/electric current)
- There are more senses than the classical five, such as balance, body position, pressure, pain, temperature,
etc. This scientific area is called psychophysics, which studies relations between the physical characteristics of
stimuli and sensory capabilities.
Stimulus Detection:
- Absolute Threshold = the lowest intensity at which a stimulus can be detected correctly 50% of the time.
Thus lower it is = greater the sensitivity.
Signal Detection Theory:
- Ppls sensitivity can fluctuate, with no fixed absolute threshold. People set their own decision criterion, a
standard of how certain they must be that a stimulus is present before they will say they detect it. This can
also change from time to time, due to several factors. Signal detection theory is concerned with these factors
that influence sensory judgements.
- Typical SD experiment: participants told a barely perceptible tone may or may not be presented after light,
creating four outcomes. When there is a sound, they can say yes/no creating a hit/miss, and when it is none
they can say yes (false alarm) or no (correct judgement).
-At low stimulus intensities, increasing rewards and costs for hits and misses will affect performance (generally
more hits)
Difference threshold = the smallest difference between two stimuli that people can perceive 50% of the time.
This is sometimes called the just noticeable difference. Weber's Law states that the difference threshold, or
jnd, is directly proportional to the magnitude of the stimulus with which the comparison is being made, and
can be expressed by the Weber Fraction.
Sensory Adaption = change over time in the responsiveness of the sensory system to a constant stimulus.
Change over time in the responsiveness of the sensory system to a constant stimulus.
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Sensory Systems
Vision = Normal stimulus for vision is electromagnetic energy, or light waves, which are measured in
The Human Eye
- Light waves enter cornea > pupil (dilates constricts amount of light entering eye) > pupil size controlled by
muscles in coloured iris > lens (becomes thinners to focus on distant object/thicker vice versa) > retina (light
sensitive multi layered tissue) > lens reverse the image in horizontal/vertical direction but brain reconstructs
visual output.
Myopia = can see near not far, nearsightedness. Eyeball usually longer bc focus infront retina.
Hyperopia = see near not far, farsightedness. Eyeball shorter bc focus behind retina.
- Aging process usually causes eyeball to shorten, which is why middle aged people get reading glasses.
Photoreceptors: The Rods and the Cones:
- The retina is actually an extension of the brain. It contains two light sensitive receptor cells: rods and cones
(due to their shapes.) 120 mill rods and 6 mill cones in each eye.
Rods = function best in dark, black/white receptors. 500x more sensitive than cones, don’t receive colour
Cones = function best in bright light, animals active during day only have cones = bad night vision
- In humans, rods found everywhere except fovea (small area in center of eye w/ only cones. The peripheral of
eye contains mainly rods.
- Msg > Bipolar cells (synaptic connection) > synapse with
ganglion cells (axons connected in bundle to form optic nerve)
> eventually funneled into only 1 traffic lane from retina
- Rods can combine their individual electrical msgs to the
bipolar cell, where the additive effect of the many signals may
be enough to fire it.
-Cones that line in periphery of retina also share bipolar cells,
but the densely packed cones have their own private line to a
single bipolar cell. This results in visual acuity, or ability to see
in fine detail, is greatest when the visual image projects
directly into fovea.
- Dark adaption is progress improvement in brightness sensitivity that occurs over time under conditions of
low light. Photoreceptors deplete during daytime due to light, but will regenerate when in darkness due to
Colour Vision:
Trichromatic theory = colour vision is based on the activity of three types of receptors, each with a different
peak sensitivity wavelength. Cones particularly sensitive to blue, green and red.
- wasn’t consistent b/c ppl with red-green colour blindness
could see yellow, the by product of those 2 colours. An
afterimage would also occur in diff colour after colour stimulus
was viewed steadily and withdrawn.
Opponent-process theory = proposed that each of the three
cone types responds to a red or green, blue or yellow, and
another to black or white. IE, chem reaction to green stimulus
with an opponent process to create red stimulus. This may
explain the colour afterimage. Activation of one member of the
pair inhibits activity in the other.
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Dual-process theory combines both to account
for the colour transduction process. Cones
contain 3 diff prtein photopigments, diff ratios of
activity can produce any hue in visible spectrum.
Process occurs in the ganglion cells and the visual
cortex of the brain.
Trichromats = norma vision.
Dichromats = deficiency in red-green or blue-
Monochromats = only black-white.
Analysis and Reconstruction of Visual Scenes
- Nerve impulse from optic nerve > thalamus > primary visual cortex. There is a point to point correspondence
between tiny regions of the retina and neurons of the visual cortex. The fovea is represented by a
disproportionately large area, due to its high visual acuity.
- Some of the neurons are organized to receive and integrate sensory nerve impulses originating in specific
regions of the retina, these are feature detectors. Hubel and Wiesel found that certain neurons fired most
frequently when lines of certain orientations were presented. The discovery of these revolutionized vision
research. IE, one neuron may fire more with a horizontal line, another in a vertical line.
- Other classes of feature detectors respond to colour, depth and movement. These subdivide a visual scene
into component dimensions. IE diff colour balls thrown at you, seperate but overlapping modules
simultaneously analyze its colours shape distance and movement by engaging in parallel processing.
- In the Visual association cortex more complex features of the scene are combined and interpreted in light of
our memories. Thus it leads to us catching the ball, as we recognize what it is. Scientists discovered neurons
selectively respond not just to basic stimuli but to complex stimuli which acquired special meaning. IE. single
neuron responded to images of Bill Clinton.
-Stimuli for our sense of hearing are sound waves, a form of mechanical energy. Sound is just pressure waves,
resulting in vibrations. These sound waves have two characteristics: Frequency and Amplitude.
- Frequency is the number of sound waves, or cycles per second. Hertz is the unit of measurement, with one
cycle per second. Higher frequency = higher perceived pitch.
-Amplitude refers to the vertical size of the sound waves - the amount of compression and expansion of the
molecules in the conducting medium. Amplitude = loudness. Unit of measurement is decibels (db)
Auditory Transduction : Pressure to nerve impulses;
- Sound waves > auditory canal > eardrum (movable membrane vibrating to response of sound wave) > middle
ear (hammer, anvil and stirrup amplifies sound waves 30x) > inner ear containing cochlea, filled with fluid and
contains basilar membrane, a sheet of tissue > resting on membrane is organ of Corti which contains hairs that
are sound receptors > tectorial membrane that overhangs basilar membrane along entire length of cochlea >
hairs synapse send impulse to auditory relay station > thalamus > auditory cortex.
- Sound wave strike ear drum > pressure at oval window > sets fluid in cochlea in motion > fluid result in
vibration in basilar membrane and membrane above it causing hair to bend in organ of Corti > trigger
neurotransmitter w/ hair cells into auditory nerve.
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