PSYCH1000: CHAPTER 5: SENSATION & PERCEPTION
Sensory Processes
• Sensation: the ways your sense organs receive/transmit info
• Perception: brain’s processing/interpretation of that info
• Psychophysics: study relation between physical stimuli and psychological responses
• Absolute threshold: lower limit of stimuli detectability (ex. how far away we detect light)
• Difference threshold: amt of change required for JND (just noticeable difference)
• Helps to determine relationship between stimuli + what is perceived
• Weber’s Law
• Size of difference threshold relative to physical intensity of test is constant (∆I/I =C)
• ∆I = difference between initial stimuli intensity and the intensity when JND reported
• I = initial stimuli intensity
• C = Weber’s Constant
• Ex. If stimuli is 50 db & you report JND at 55 db, (5/50 —> Weber’s constant is 1/10)
• ∴ at 100db, we can expect JND at (by back calculating ∆I)
• Smaller C value = more sensitive system
• Fechner’s Law (father of psychophysics)
• Sensation increases w/ the logarithm of intensity (doesn’t agree w/ Weber’s linear theory)
• S = k (logI)
• Steven’s Power Law
• S = k log IN
• This is the best one
• Subliminal stimuli: not consciously perceived
• Subliminal cuts: advertisers adding subliminal messaging to influence consumers
• Doesn’t actually impact consumer behaviour as far as we know
• However: priming does actually tend to influence people (even if it is not perceived)
• Minimum time for a neural response is faster than minimum time for perception
• Adaptation occurs in response to unchanging stimuli
• Senses are classified by energy to which they respond
Commonalities Between Sensory Systems
1. Accessory structures: channel info to more sensitive areas (eg, outer ear)
2. Transduction: receptors turn external info into neural info
3. Coding: (for intensity), eg frequency
4. Interaction: senses bleed into one another (eg. smell in tasting)
Sensory Systems: Vision
• Stimulus: electromagnetic energy / light waves
PARTS OF THE EYE
• Iris: contracts and changes opening of pupil (impacts how much light gets in)
• Cornea : clear protective cover, focuses image
• Lens: fine tunes (focuses either near or far distance)
• Vitreous humour: jelly in eyeball, keeps shape of ball, pressurizes inside of eye
• Retina: turns light into vision, has receptors on it
• Fovea: most sensitive part of retina
• Optic nerve: bundle of axons from cells in retina that exit eye
• Blind spot: where optic nerve leaves eye, no receptors —> no vision perceived
• Ganglion cells: big cells on retina where axons form optic nerve, output
• Bipolar cells: connected to both ganglion and receptors, collect and pass along info
• Receptor cells: light-sensitive, in retina, where transduction occurs
• Rods: brightness receptors
, • Cones: colour receptors
• Photopigments: proteins in receptor cells which convert light to nerve impulses via
chemical reactions
• Dark adaptation: gradual regeneration of depleted photopigments after bright illumination
• Spectral sensitivity: showing which cones are sensitive to which colours (wavelengths)
• Colour vision
• Trichromatic Theory
• Colour vision is based on activity of 3 types of receptors, each w/ a different peak
sensitivity (short, med, long wavelength) —> red, green, blue
• Balance of activity in S/M/L cones determines perception of colour
• Opponent-Process Theory
• Cone photoreceptors are linked to form 3 opposing colour pairs (blue/yellow, red/green,
black/white)
• Activity in one member of the pair inhibits activity in the other
• This explains why you can’t describe a colour as “bluish yellow” or “reddish green”
• When one member of the pair is “fatigued” by extended exposure, inhibition of the
other member lessens (can lead to this colour being perceived)
• Colour-deficient vision
• Dichromat: someone who has a deficiency in either red-green or yellow-blue systems
(absence of hue-sensitive photopigment in certain cones)
• Monochromat: someone who is only sensitive to black-white system (total colour
blindness)
• Visual info analyzed by feature detectors in primary visual cortex
• Stimulus elements reconstructed/interpreted in visual association cortex
How Do Rods & Cones Work?
• Horizontal cells between bipolar and receptors (inhibitory)
• Amacrine cells between ganglion and bipolar (inhibitory)
• Many more rods than cones
• Rods: operate at low light intensity (sensitive to brightness)
• Fovea does not contain any rods (if you’re looking right at something, less sensitive to light)
• Monochrome (no colour vision)
• Visual pigment called rhodopsin
• Cones: operates at higher intensity (less sensitive to light)
• Concentrated in fovea
• Full colour
• One of 3 photopigments: chlorolabe (Green), erythrolabe (Red), cyanolabe (Blue)
• Responsive to different wavelengths (colour)
• Duplex theory : 2 kinds of visual receptors
• Visual pigments react to light (break down in the presence of light and split into chemicals
which cause action potentials)
• Single cell recording: isolate a single retinal ganglion cell and attach a micro electrode and
record output
• find spot in visual field where ganglion cell is firing the most (thats the area thats served by
that ganglion cell) —> helps us plot a receptive field for a particular ganglion cell
• horizontal cells inhibit the ganglion cell (slow firing rate) right before it hits the hot spot
(areas of max/min response circles) & returns to base firing rate once leaves receptive field
• Lateral inhibition: as one receptor gets activated a lot, it activates horizontal inhibitors and
inhibits next door receptor from firing (helps to enhance / clean up image)
• That is how a ganglion cell’s receptive field is built
Sensory Systems: Audition
• Stimulus: sound waves
Sensory Processes
• Sensation: the ways your sense organs receive/transmit info
• Perception: brain’s processing/interpretation of that info
• Psychophysics: study relation between physical stimuli and psychological responses
• Absolute threshold: lower limit of stimuli detectability (ex. how far away we detect light)
• Difference threshold: amt of change required for JND (just noticeable difference)
• Helps to determine relationship between stimuli + what is perceived
• Weber’s Law
• Size of difference threshold relative to physical intensity of test is constant (∆I/I =C)
• ∆I = difference between initial stimuli intensity and the intensity when JND reported
• I = initial stimuli intensity
• C = Weber’s Constant
• Ex. If stimuli is 50 db & you report JND at 55 db, (5/50 —> Weber’s constant is 1/10)
• ∴ at 100db, we can expect JND at (by back calculating ∆I)
• Smaller C value = more sensitive system
• Fechner’s Law (father of psychophysics)
• Sensation increases w/ the logarithm of intensity (doesn’t agree w/ Weber’s linear theory)
• S = k (logI)
• Steven’s Power Law
• S = k log IN
• This is the best one
• Subliminal stimuli: not consciously perceived
• Subliminal cuts: advertisers adding subliminal messaging to influence consumers
• Doesn’t actually impact consumer behaviour as far as we know
• However: priming does actually tend to influence people (even if it is not perceived)
• Minimum time for a neural response is faster than minimum time for perception
• Adaptation occurs in response to unchanging stimuli
• Senses are classified by energy to which they respond
Commonalities Between Sensory Systems
1. Accessory structures: channel info to more sensitive areas (eg, outer ear)
2. Transduction: receptors turn external info into neural info
3. Coding: (for intensity), eg frequency
4. Interaction: senses bleed into one another (eg. smell in tasting)
Sensory Systems: Vision
• Stimulus: electromagnetic energy / light waves
PARTS OF THE EYE
• Iris: contracts and changes opening of pupil (impacts how much light gets in)
• Cornea : clear protective cover, focuses image
• Lens: fine tunes (focuses either near or far distance)
• Vitreous humour: jelly in eyeball, keeps shape of ball, pressurizes inside of eye
• Retina: turns light into vision, has receptors on it
• Fovea: most sensitive part of retina
• Optic nerve: bundle of axons from cells in retina that exit eye
• Blind spot: where optic nerve leaves eye, no receptors —> no vision perceived
• Ganglion cells: big cells on retina where axons form optic nerve, output
• Bipolar cells: connected to both ganglion and receptors, collect and pass along info
• Receptor cells: light-sensitive, in retina, where transduction occurs
• Rods: brightness receptors
, • Cones: colour receptors
• Photopigments: proteins in receptor cells which convert light to nerve impulses via
chemical reactions
• Dark adaptation: gradual regeneration of depleted photopigments after bright illumination
• Spectral sensitivity: showing which cones are sensitive to which colours (wavelengths)
• Colour vision
• Trichromatic Theory
• Colour vision is based on activity of 3 types of receptors, each w/ a different peak
sensitivity (short, med, long wavelength) —> red, green, blue
• Balance of activity in S/M/L cones determines perception of colour
• Opponent-Process Theory
• Cone photoreceptors are linked to form 3 opposing colour pairs (blue/yellow, red/green,
black/white)
• Activity in one member of the pair inhibits activity in the other
• This explains why you can’t describe a colour as “bluish yellow” or “reddish green”
• When one member of the pair is “fatigued” by extended exposure, inhibition of the
other member lessens (can lead to this colour being perceived)
• Colour-deficient vision
• Dichromat: someone who has a deficiency in either red-green or yellow-blue systems
(absence of hue-sensitive photopigment in certain cones)
• Monochromat: someone who is only sensitive to black-white system (total colour
blindness)
• Visual info analyzed by feature detectors in primary visual cortex
• Stimulus elements reconstructed/interpreted in visual association cortex
How Do Rods & Cones Work?
• Horizontal cells between bipolar and receptors (inhibitory)
• Amacrine cells between ganglion and bipolar (inhibitory)
• Many more rods than cones
• Rods: operate at low light intensity (sensitive to brightness)
• Fovea does not contain any rods (if you’re looking right at something, less sensitive to light)
• Monochrome (no colour vision)
• Visual pigment called rhodopsin
• Cones: operates at higher intensity (less sensitive to light)
• Concentrated in fovea
• Full colour
• One of 3 photopigments: chlorolabe (Green), erythrolabe (Red), cyanolabe (Blue)
• Responsive to different wavelengths (colour)
• Duplex theory : 2 kinds of visual receptors
• Visual pigments react to light (break down in the presence of light and split into chemicals
which cause action potentials)
• Single cell recording: isolate a single retinal ganglion cell and attach a micro electrode and
record output
• find spot in visual field where ganglion cell is firing the most (thats the area thats served by
that ganglion cell) —> helps us plot a receptive field for a particular ganglion cell
• horizontal cells inhibit the ganglion cell (slow firing rate) right before it hits the hot spot
(areas of max/min response circles) & returns to base firing rate once leaves receptive field
• Lateral inhibition: as one receptor gets activated a lot, it activates horizontal inhibitors and
inhibits next door receptor from firing (helps to enhance / clean up image)
• That is how a ganglion cell’s receptive field is built
Sensory Systems: Audition
• Stimulus: sound waves
