Chapter 5 – Sensation & Perception
Synesthesia: Mixing of the senses; experiencing colours as touch or having different shapes.
Transduction: Process of translating information via sensory receptors into language of nerve
impulses. - Feature detectors: breakdown and analyze the specific features of the stimuli.
Binding problem: Sensations and perception blend together so completely that they are difficult to
Difference between Sensation & Perception
Sensation: the stimulus-detection process that our sense organs respond to & translate stimuli into nerve
impulses (that are sent to the brain). Answering: What is the stimulus?
Perception: Making ‘sense’ of what our senses tell us – the active process of organizing this stimulus
input and giving it meaning. Answering: What does this ‘sense’ mean?
One’s interpretation, or perception, is influenced by their context: can be interpreted differently
depending on creativity
Sensation/ Sensory Processes
Transduction: the process whereby the characteristics of a stimulus are converted into nerve impulses
2. Audition (hearing)
3. Touch: Pain, temperature, pressure
4. Gustation (taste)
5. Olfaction (Smell)
Psychophysics Ө Studies the relations between the physical characteristics of stimuli and
sensory capabilities, is concerned with 2 kinds of sensitivities
1) Concerns the absolute limits of sensitivity (ie. softest sound humans can detect?)
2) Sensitivity between different stimuli (ie. smallest difference of brightness that can be
detected, or changes in weight? –The difference threshold
Stimulus Detection: The Absolute Threshold
The Absolute threshold: The lowest intensity at which a stimulus can be detected correctly
50% of the time.
- Thus: The Lower the absolute threshold = The Greater the sensitivity
Decision criterion: a standard of how certain an individual must be that a stimulus is present
before they will say they detect it
Signal Detection Theory: The concern with the factors that influence sensory judgements
Subliminal Stimulus: A stimulus that is so weak or brief that, although it is received by the sense, it
cannot be perceived consciously; below the absolute threshold
- Can the stimuli affect attitudes and behaviours without our knowledge of it?
- James Vicary: Test of Popcorn sales Individuals associate unpleasant or pleasant subliminal stimuli expressed somewhat negative or positive
attitudes toward an idea/person; indicating a process of subconscious attitude conditions (whether
positive or negative).
- Philip Merike – argue that the effect is one of biasing perception
Subliminal cues can bias what we perceive at a conscious level & may alter our conscious
experience of those stimuli.
The Difference Threshold
The Difference Threshold (Just noticeable difference): Defined as the smallest difference
between two stimuli that people can perceive 50% of the time.
Weber’s Law: States that the difference threshold is directly proportional to the magnitude of
the stimulus with which the comparison is being made; Weber Fraction.
A. Audition (Tonal Pitch) – 1/333
B. Vision (Brightness of white light) – 1/60
C. Kinesthesis (lifting weights) – 1/50
D. Pain (Heat produced) – 1/30
E. Audition (Loudness) – 1/20
F. Touch (pressure applied to skin) – 1/7
G. Smell (India rubber) – ¼
H. Taste (Salt concentration) 1/3
Sensory Adaptation: Sensory neurons are engineered to respond to a constant stimulus by decreasing
their activity; therefore diminishing sensitivity to an unchanged stimulus is adaptation
- This occurs even with eyesight/vision: Tiny involuntary eye movements keep images moving
about the retina, or else stationary objects would simply fade from sight if we stared at them.
The Sensory Systems
The normal stimulus for vision is
electromagnetic energy, or light
waves, which are measured in
nanometers (or one billionth of a
The Human Eye
1. Cornea: A protective structure at the front of the eye, where light waves enter the eye through cornea
– First Layer.
2. Pupil: An adjustable opening that can dilate or constrict- Behind the Cornea. It controls the amount
of light that enters the eye 3. Iris: Muscles in the coloured iris control the pupil’s size (surrounding the Pupil).
4. Lens: An elastic structure that becomes thinner to focus on distant objects and thicker to focus on
nearby objects – Behind the Pupil.
- Reverses the image (up-side-down) onto the retina
- Dictates the clearness & focus of the image
5. Retina: A multilayered tissue at the rear of the fluid-filled eyeball.
Myopia – Nearsightedness: focus is in front
of the retina (too near the lens).
- Causes blurriness for faraway objects
Hyperopia – Farsightedness: When the lens
does not thicken enough and the image is
focused on a point behind the retina (too far
from the lens)
1) Photoreceptors: The Rods and Cons
Rods: Function best in dim light; primarily
black and white brightness receptors
- 500 Times more sensitive to light than
cones but, do not sense colours
Cones: Colour receptors; function best in
Rods and Cones’ light-sensitive ends point away from the direction of the entering light so they
only receive a fraction of the light energy entering the eye. They share bipolar cells so that they
can ‘funnel’ their individual electrical messages to bipolar cells.
Fovea: Small area in the centre of the retina that only contain Cones – cones decrease in concentration
away from the centre of the retina. Rods are found throughout the retina except in the fovea.
- Our visual acuity (the ability to see fine detail) happens best in the fovea because of the ‘private line’
of single bipolar cells found only in the fovea.
2) Bipolar Cells: have synaptic connections with rods and cons; they synapse with a layer of about a
million 3) Ganglion cells - whose axon are collected into a bundle to for the Optic Nerve.
Optic Nerve: Formed by axons of the ganglion cells at the back of the eye – producing an Optic Disc or
blind spot where no photoreceptors can exists. Our perceptual system ‘fills in’ the missing info.
Visual Transduction: From Light to Nerve Impulses
Transduction – The process whereby the characteristics of a stimulus are converted into nerve impulses.
Photopigments –Proteins molecules that Rods and Cones use to translate light waves into nerve impulses Dark Adaptation: The progressive improvement in brightness sensitivity that occurs over time under
conditions of low illumination. The rods, whose photopigments regenerate more slowly, do not reach
their maximum sensitivity for about half an hour.
The Trichromatic Theory (Additive colour mixture): Young-Helmholtz (1800) - There is three types
of colour receptors in the retina. Although all cones can be stimulated by most wavelengths to
varying degrees, individual cones are most sensitive to wavelengths that correspond to either,
blue, green, or red.
- (Light) If all three cones are equally activated, a pure white colour is perceived.
- Afterimage: an image in a different colour appears after a colour stimulus has been viewed
steadily and then withdrawn
Opponent-Process Theory: Ewald Hering (1870) – Proposed that each of the three cone types respond
to two different wavelengths.
1) Red or Green
2) Blue or Yellow
3) Black or White
- When staring at a black & green surface, the neural processes that register these colours become
fatigued. So when you gaze at a white surface, which reflects all wavelengths, a ‘rebound’
opponent reaction occurs as each receptor responds with its opposing white & red reactions.
Dual Processes in Colour Transduction: Combination of trichromatic and opponent-process theories
to account for colour transduction process.
- Different ratio of activity in the red-, blue-, and green- sensitive cones can produce a pattern of
neural activity that corresponds to any hue in the spectrum. - Certain ganglion cells in the retina & neurons in visual relay stations and visual cortex, respond
in an opponent-process fashion by altering their rate of firing. Ie. Red – respond at a high rate but
green will cause the same cell to fire at a lower rate.
a) Trichromat – Normal colour vision, sensitive to all colours
b) Dichromat – A person who is colour-blind in only one of the systems (red-green or yellow-blue)
c) Monochromat – Sensitive only to black-white system and is totally colour-blind
Primary Visual Cortex: in the occipital lobe at the rear of the brain.
Feature Detectors: Group of neurons within the primary visual cortex that are organized to receive and
integrate sensory nerve impulses originating in the retina.
- They fire selectively in response to stimuli that have specific characterises: certain neurons fire more
frequently when lines or certain orientations are presented, & detecting response to colours, depth or
movement (Parallel processing – information and constructing a unified image of properties).
Visual Association Cortex: Final stages in process of constructing a visual representation occur when
the information analyzed and recombined by the primary visual cortex is routed to other cortical
regions. – Visual scenes are combined and interpreted in light with memories & knowledge.
*This links what we see & “recognize” to – what it “is”
Sound: Stimuli for our sense of hearing are sound ways (form of mechanical energy). They are pressure
waves in the air, water, or some other conducting medium.
- Speed: Approx. 1,200 Km/Hour
Frequency: The Number of sound waves, or cycles, per second
o Hertz (Hz): The technical measure of cycles per second. Humans are capable of
detecting sound frequencies from 20-20,000 hertz (12000 hertz in older people).
Amplitude: Refers to the vertical size of sound waves – the amount of compressions and
expansion of the molecules in the conducting medium. Measured by Loudness
o Decibels (db): A measure of the physical pressures that occur at the eardrum. The
absolute threshold for hearing is from 0 decibels, & increases by 10 decibels (tenfold)
increase in loudness.
Middle Ear contains 3 bones that translate pressure waves into nerve impulses. The activity of these
bones amplified the sound waves more than 30 times.
1) Malleus (Hammer): Attached firmly to the eardrum
2) Incus (Anvil)
3) Stirrup (Stapes): Attached to the oval window, which forms the boundary between the middle
ear and the inner ear.
The Inner Ear contains: The Cochlea - a coiled, snail shaped tube filled with fluid and contains the basilar membrane, a sheet
of tissue that runs its length.
Organ of Corti - Rests on the basilar membrane, it contains about 16000 tiny hair cells that are the
actual sound receptors. The hair cells synapse with the neurons of the auditory nerve which sends
impulses via an auditory relay station in the thalamus to the auditory cortex (located in the
Sound waves Ear Drum (3 bones) Cochlea (Fluid movement) Organ of Corti (Bending hairs)
Neurotransmitters (release) Synaptic space (between hairs) Neurons of the Auditory Nerve
Nerve impulses Brain
Coding of Pitch and Loudness
The Auditory system – transforms the sensory qualities of loudness and pith into the language of nerve
High-amplitudes: Hairs bent more and release more neurotransmitters = high rate of firing within
the auditory nerve. Certain receptor neurons have higher thresholds than others (intense sounds).
The coding of pitch involves two different processes:
1) Frequencies below 1000 hertz
2) Higher frequencies
Frequency Theory of pitch perception: Nerve impulses sent to the brain match the frequency
of the sound wave. Ie. 30 hertz = 30 volleys of nerve impulses/second.
Place Theory: (Georg von Bekesy – uses guinea pigs) Suggests that the specific point in the
cochlea where the fluid wave peaks and most strongly bends the hair cells serves as a
frequency coding cue. Uses mapping of location to determina