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Chapter 4

PSYCH101 Chapter Notes - Chapter 4: Optic Chiasm, Far-Sightedness, Prosopagnosia

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Sensation & Perception Textbook
4.1 Sensory and Perception
Sensation: detecting external events by sense organs and turning stimuli into neural signals
Transduction: specialized receptors transform physical energy into neural impulses,
becomes inner representation of the world
Perception: organizing and interpreting sensed stimuli
Doctrine of Specific Nerve Energies: different senses sent to different areas in the brain
Proposed by Johannes Muller
Overlapping sensations pruned by age 3 - brain pathways become more distinct
Orienting Response: quick shift of attention from stimuli that signals change in senses
Sensory adaptation: reduced activity in sensory receptors with repeated exposure to a stimuli
Psychophysics: how physical energy (eg. light, sound) and their intensity relate to psychological
experience (William Gustav Fechner)
Absolute threshold: minimum amount of energy or quantity of a stimulus required to
be detected at least 50% of times presented
Difference threshold: smallest difference between stimuli reliably detected at least 50%
of times presented
Depends on intensity of original stimulus
Signal detection theory: stimulus
is perceived based on both
sensory perception and
judgement made by subject
(sensory and decision process)
Subliminal messages: can
enhance/activate already existing
motivational state, but cannot create a
new one
Gestalt: the whole is more than the sum
of its parts
Create different sensory
Top-down processing: perceptions
influenced by expectations or prior

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Sensation & Perception Textbook
E.g. hearing messages in songs after being told what to listen for
Bottom-up processing: perceive individual bits of sensory information and use them to
construct more complex perception (e.g. sounds to message)
Unfamiliar or difficult to recognize
Perceptual set: filter influencing aspects of scene given our attention, and others ignored
Divided attention: paying attention to more than one stimulus simultaneously
Selective attention: focusing on one particular event or task
Inattentional blindness: not noticing clearly visible events because attention directed elsewhere
4.2 Visual System
Vision comes from light waves on electromagnetic spectrum
Wavelength - hue of colour (red-blue)
Amplitude - dim or bright colours (intensity)
Many wavelengths clustered around one colour - vivid
Large variety of wavelengths - “washed out”
Structure of the eye
Sclera: white, outer surface of the eye
Cornea: clear layer that covers the front portion of the eye; contributes to eye’s ability to focus
Pupil: regulates amount of light that enters by changing its size
Dilates (expands) to allow more light to enter and constricts (shrinks) to allow less light
Iris: round muscle that adjusts the size of the pupil; the colour part of the eyes
Lens: behind the pupil, a clear structure that focus light onto the back of the eye
Accommodation: lens change shape to ensure light is refracted so it’s focused when it
reaches the back of the eye
Transduction occurs at the back of the eye
with the retina
Retina: lines the inner surface of the eye and consists
of specialized receptors that absorb light and send
signals related to the properties of light to the brain
Photoreceptors: where light will be
transformed into neural signals for brain to
Rods: occupy peripheral regions of
retina; highly sensitive under yellow
light levels, making it responsive to
black and grey
Ten-to-one ratio with
ganglion cells
Cones: sensitive to different wavelengths of light that we perceive as colour
Clustered around fovea: central region of retina
One-to-one ratio with ganglion cells
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