PSYC 1010 Chapter Notes - Chapter 4: Detection Theory, Absolute Threshold, Subliminal Stimuli
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Chapter 4- Sensation and Perception3/23/2012 5:48:00 PM
Sensation- the stimulation of sense organs. Involves absorption of energy.
Perception- the selection, organization, and interpretation of sensory input.
Involves organizing and translating sensory input into something meaningful
Psychophysics- the study of how physical stimuli is translated into
psychological experience. Sensation begins with a stimulus.
Threshold- a dividing point between energy levels that do and do not have
Absolute threshold- for a specific type of sensory input is the minimum
amount of stimulation that an organism can detect. Defines the boundaries
of an organism’s sensory capabilities.
Just noticeable difference [JND]- the smallest difference in the amount of
stimulation that a specific sense can detect. Its basically the absolute thresh.
Weber’s Law- the size of a just noticeable difference is a constant proportion
of the size of the initial stimulus. Constant proportion is called Weber’s
fraction. As stimuli increase in magnitude, the JND becomes larger.
Fechner’s law- the magnitude of a sensory experience is proportional to the
number of JND’s that the stimulus causing the experience is above the
absolute threshold. Increments in stimulus intensity produce smaller and
smaller increases in the perceived magnitude of sensation.
Ex: There are three different light bulb intensities, each are progressively
brighter. You turn on the first bulb, turn it off, turn on the second one, turn
off the light, and turn on the third one. Although each light bulb is brighter
than the last, you don’t see a difference. Concludes that perception can’t be
measured on absolute scales since everything is relative.
Signal- detection theory- detection of stimuli involves decision processes,
which are both influenced by a variety of factors besides stimulus intensity.
Subliminal perception- the registration of sensory input without conscious
awareness (below threshold).
Sensory adaptation- a gradual decline in sensitivity due to prolonged
stimulation. It is an automatic, built-in process that keeps people tuned in to
the changes rather than the constants in their sensory input. It allows
people to focus on the changes in the environment so they can respond to
threats quickly. This is a behavioural adaptation preserved by nat. selection.
Lens- the transparent eye structure that focuses the light rays falling on the
retina. It can cause accommodation, focusing light on objects more.
Nearsightedness- close objects are seen clearly but distant objects are blurry
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Farsightedness- distant objects are seen clearly but close objects appear
Retina- the neural tissue lining the inside back surface of the eye; it absorbs
light, processes images, and sends visual information to the brain.
Optic disk- a hole in the retina where the optic nerve fibers exit the eye.
Cones- specialized visual receptors that play a key role in daylight vision and
colour vision. Great at providing sharpness and precise detail than rods.
Fovea- a tiny spot in the center of the retina that contains only cones.
Rods- specialized visual receptors that play a role in night and peripheral vis.
Dark Adaptation- the process in which the eyes become more sensitive to
light in low illumination. From outside-> going into dark theater.
Light Adaptation- the process whereby the eyes become less sensitive to
light in high illumination. Dark theater -> going outside.
Receptive field of a visual cell- the retinal area that, when stimulated, affects
the firings of that cell.
Lateral antagonism (lateral inhibition)- occurs when neural activity in a cell
opposes activity in surrounding cells. Responsible for the opposite effects
that occur when light falls on the inner versus outer portions of center-
surrounded receptive fields. Allows the retina to compare the light falling in a
specific area against general lighting. Make out shapes and objects.
Optic chiasm- the point at which the optic nerves from the inside half of
each eye cross over and then project to the opposite half of the brain.
Parallel processing- simultaneously extracting different kinds of information
from the same input.
Visual agnosia- the inability to recognize familiar objects.
Subtractive colour mixing- works by removing some wavelengths of light,
leaving less light than was originally there. Mixing paint for example.
Additive colour mixing- works by superimposing lights, putting more light in
the mixture than exists in any one light by itself. Shining 3 different lights.
Trichromatic theory of colour vision- the human eye has three types of
receptors with different sensitivities to different light wavelengths.
Opponent process theory of colour vision- colour vision depends on receptors
that make antagonistic responses to three pairs of colours.
Reversible figure- a drawing that is compatible with two interpretations that
can shift back and forth.
Perceptual set- a readiness to perceive a stimulus in a particular way.
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