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Chapter 5

Psychology 1000 Chapter 5: Chapter 5

Course Code
PSYCH 1000
John Campbell

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Psych 1000: Chapter 5
Sensation and Perception:
Info comes in through our senses
Transduction: your sensory receptors must translate this info into the only language
your nervous system understands … nerve impulses
Neurons called feature detectors break down and analyze the specific features of the
o Stimuli pieces are reconstructed into a neural representation that is compared
with already stored info
Our brains interpret this info
o You look with your eyes
o You see with your brain
o Stimulus-detection process
o Organs translate stimuli into nerve impulses
Perception: making sense of what our senses tell us is the active process of
organizing this stimulus input and giving it meaning
o Organizes and giving meaning to input
o The same sensory input may be perceived in different ways at different times
Mixing of the senses
Women are more likely to be synaesthetes
Provides a glimpse of how we “sense” and “understand” the world
There is a cross wiring in the visual cortex
Theory #1 = pruning of neural connections that occurs in infancy has not occurred
o Diffusion tensor imaging which lights up white matter pathways in the brain has
revealed increased connectivity in patients with synaesthesia
Theory #2 = deficit in neural inhibitory processes in the brain (binding problem)
o Create additional perceptions
Sensory Processes:
Vision, audition, touch, gustation, olfaction
Touch pressure, pain, temperature
The immune system also has sensory functions that allow it to detect foreign invaders
and to receive stimulation from the brain
Sensory processes are designed to extract from the environment the info we need to
function and survive
Psychophysics: studies relations between the physical characteristics of stimuli and
sensory capabilities, is concerned with two kinds of sensitivity
o First controls absolute limits

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The Contribution of Context:
Change in context results in a change in perception
The Stroop Effect:
The colour activity
Our perception of the colour becomes conflicted when the words do not match the
colours we are seeing
Absolute Threshold:
Intensity at which a stimulus can be detected 50% of the time
Lower the absolute threshold, the higher the sensitivity
A key distinction here is that absolute threshold measures the level that we can actually
report sensing a stimuli
We have to be consciously aware of the stimuli to successfully report it
Subliminal Perception:
A stimulus that is so weak or brief that, although it is received by the senses, it cannot
be perceived consciously
The stimulus is below the absolute threshold
James Vicary, arranged to have subliminal messages flashed on a theatre screen
during a movie (drink Coca-Cola, eat popcorn)
o Popcorn sales increased by 50%
o Soft-drink sales increased by 18%
The public was outraged, fear of brainwashing (national association of broadcasters
outlawed subliminal messages on American TV)
o Vicary’s results failed to be replicated
o Admitted later that his study was a hoax to revive his advertising agency
Subliminal messages didn’t really change consumer behaviour (very subtle effects)
Research started to focus on more subtly processes, like our attitudes
Signal Detection Theory:
Peoples apparent sensitivity can fluctuate quite a bit (no fixed absolute threshold)
Decision criterion: a standard of how certain they must be that a stimulus is present
before they will way they detect it
Signal detection theory: is concerned with the factors that influence sensory judgements
At low stimulus intensities, both the participants’ an the situation’s characteristics
influence the decision criterion
Experience also plays a role in signal detection
Perception is in part a decision
The Difference Threshold:
Is defined as the smallest difference between two stimulus that people can perceive
50% of the time (just noticeable difference)

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Weber’s law: 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 as a
weber fraction
o Providing a reasonable barometer of our abilities to discern differences in the
various sensory modalities
o Humans are highly sensitive to differences in the pitch of sounds but far less
sensitive to loudness differences
Sensory Adaptation:
Sensory neurons are engineered to respond to a constant stimulus by decreasing their
Sensory adaptation: the diminishing sensitivity to an unchanging stimulus
Adaptation occurs in all sensory modalities including vision
R.M. Pritchard tiny projector attached to contact lens (when an image was projected
it began to vanish over time and reappear as parts of the original stimulus)
o Frees our senses from the constant and the mundane to pick up informative
changes in the environment
Sensory adaptation was mostly absent in animals while they were alert and engaged in
a behavioural learning task
Normal stimulus for vision is electromagnetic energy, or light waves which are
measures in nanometers
Our visual system is sensitive only to wavelengths extending from about 700-400
Light waves enter the eye through the cornea (behind the cornea is the pupil)
Pupil: control the amount of light that enters the eye
o The size is controlled by muscles in the coloured iris
Lens: an elastic structure that becomes thinner to focus on distant objects and thicker to
focus on nearby objects
Retina: a multi-layered tissue at the rear of the fluid-filled eyeball
Fovea: a small area in the centre of the retina that contains only cones
Bipolar cells: have synaptic connections with the rods and cones
Ganglion cells: axons are collected into a bundle to form the optic nerve
Myopia and Hyperopia:
o Nearsightedness
o Eyeball is longer back to front
o Lend focuses light in front of retina
o Difficulty seeing far away objects
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