TOPIC 5: SENSATION Flashcards
sensation
encoding environment energy or chemicals in terms of neural signals.
Perception
organization and interpretation of neural signals.
Psychophysics
the study of relation between physical quantities and physiological experience.
Absolute threshold
weakest stimulus detected 50% of the time.
subliminal stimulation
hypnosis or hoax?
– “subliminal” perceived up to 49% of the time.
– what about stimulineverconsciously perceived?
James Vicary (1957)
- reportedly showed 0.03 second messages repeatedly during a movie.
Murphy and Zajonc (1993)
will subliminal stimuli enter our awareness??
- presented Chinese characters preceded by subliminal faces.
- ratings of characters depended on facial expressions. (smiles=positive)
CBC showClose-Upto subliminal messages (1958)
- replicated study and no effect on behaviour .
difference threshold (just noticeable difference or JND)
smallest difference between two stimuli detected 50% of time.
JND increases as ..
JND increases as stimulus intensity increases.
Weber’s Law (1834)
JND is a constant proportion of stimulus intensity.
scaling
how does our experience change as intensity changes?
example: are two identical light bulbs twice as bright as one?
Fechner’s Law
sensory experience is proportional to the number of JNDs a stimulus is above threshold.
Fechners formula
S=kloge(I)
S = sensory experience, k= Weber fraction, I= stimulus intensity
problems with Fechner’s and Weber’s law
- less accurate approaching absolute threshold
- less accurate with increase intensity
- observers response bias confound attempts to measure sensitivity, due to time of day, fatigue
Steven Power Law (1961)
uses magnitude estimation technique:
1) observer given standard stimulus, and certain value.
2) observer assigns values to other stimuli.
Steven Power Law Formula
S=aI^b
S= sensory experience a= constant I= stimulus intensity b= exponent
evolutionary adaptive significance
- pain quickly becomes very aversive (b>1)
- accurate estimation of length and distance (b=1)
- large range of light intensities can be perceived (b<1)
Signal Detection Theory
uses catch trials; no stimulus presented 50% of the time.
- determines observers response bias
- applies statistical methods to separate sensitivity from confounding factors
- does not determine a threshold
Vision
- Transduction of photons (light energy) to neutral impulses
Visible light
narrow slice of electromagnetic spectrum; exhibits properties of particle and wave characteristics .
Distal Stimulus
Object in the world
Proximal Stimulus
pattern of energy impinging on receptors
How does travel through the eye ?
cornea
===> pupil (iris)
===> crystalline lens
===>retina
Accommodation
lens changes its shape, which changes its focal length, keeping image focused on retina.
Receptors
rods and cones (contain photochemical)
Optic disk
hole where optic nerve exits; no receptors; BLIND SPOT
Fovea
for directed looking; contains only cones.
Sensory Adaption
experience of sensation changes with prolonged exposure.
Dark Adaption
rods lose sensitivity in bright light; regenerate bleached photopigment in - 20 mins.
Trade Off
adaption may decrease sensitivity to unchanging stimuli, BUT allows perception of important environmental changes.
Retina
area on the retina that, in reaction to a stimulus, influences the firing of a neutron.
primary visual cortex
- Hubel and Wiesel recorded cats brains
- Located in the occipital lobe
- Simple cells
- complex cells
- hypercomplex
(end-stopped) cells - includes feature detectors
simple cells
triggered by pattern in receptive field, such as a bar of light with certain width, orientation, and location.
complex cells
also requiring motion in specific direction
hypercomplex cells
must also have particular length
or moving corners/angles
feature detectors
groups of neurons within the primary visual cortex are organized to receive and integrate sensor nerve impulses originating in specific regions of the retina.
visual association cortex
- parallel processing areas
- part of distinct cortical pathways. ventral and dorsal ,what and where.
parallel processing areas
- handle shape, colour, motion, and depth.
- shape and color are processed in the form perception regions .
- motion and depth are processed in location/movement perception regions.
“what” pathway/ventral stream
specialized for perceiving shapes and identifying objects
“where” pathway/dorsal stream
specialized for perceiving spatial relationships and guiding actions (how?)
prosopagnosia
inability to perceive or identify faces; caused by damage to the fusiform face area in ventral stream
cerebral achromatia
colour blindness due to cortical damage to colour area in ventral stream
akinetopsia
deficit in perceiving motion of objects; due to damaged motion area in dorsal stream
Balint’s syndrome
person can identify individual objects, but cannot tell where they are located or reach for them (intact “what” pathway, but damaged “where” pathway?)
visual form agnosia
person cannot “see” (perceive or or identify) objects, but may be able to reach out and grasp them (damaged “what” pathway, but intact “where” pathway?)
color perception
- evolved to aid object perception, defeat camouflage
- visible wavelengths between 380-720
Trichromatic theory
- Thomas Young, 1802; von Helmholtz
- only a few different types of receptors required, each sensitive to different wavelengths
- catch: you can’t combine two of the primary colours to make a third (red, green, blue)
- evidence: there are different types of cones.
Opponent-process theory
- Edward Hering
- proposed that each of the three cone types respond to two different wavelengths.
- problem: we don’t have yellowfins cones or receptors.
evidence of Opponent-process theory
- afterimage
- simultaneous color contrast
afterimage
negative image experiences adapting to a color stimulus. as you stare at a color, the neural processes become fatigued, when you cast your eyes on a white surface, the opponent color will appear.
simultaneous colour contrast
surrounding an area with a colour changes the appearance of the surrounded area
3 types of cones
- One type responds to red or green
- Another type responds to blue or yellow
- The last responds to white or black
dual-process theory
combine opponent-process theory and trichromatic theory
- trichromatic theory is right about receptors
- opponent-process theory is right about processing.
what is color deficiency caused by
caused by an absence of hue-sensitive photopigment in certain types.
Trichromats
people with normal color vision and are sensitive to all three systems: red-green, blue-yellow, black-white.
Dichromate
a person who is color blind to only one of these systems.
Monochromat
sensitive only to black-white system and is totally colorblind.
Distal stimulus
vibrating source, moving air molecules
Proximal stimulus
kinetic energy arriving at eardrum
energy range
0.0002-200 dynes/cm2; logarithmic scale used: decibels (dB)
sound travel through the :
pinna==> ear canal==> eardrum==>ossicles ==> cochlea
what is the auditory nerve comprised of ?
comprised of the axons of hair cells
what do the axons of the hair cells do?
projects to subcortical structures before going to the primary auditory cortex in the temporal lobe
what does the middle ear house?
the ossicle which are the three smallest bones.
- Malleus (hammer)
- Incus (anvil)
- Stirrup (stapes)
what does the inner ear contain?
- Cochlea
- Basilar membrane
- Organ of Corti
Cochlea
a coiled tube hat is filled with fluid and contains the basilar membrane
Basilar membrane
a sheet of tissue that runs its length.
Organ of Corti
rests on top of the basilar membrane, contains the hair cells that are the actual sound receptors.
what do the hair cells synapse with
the auditory nerve
pitch coding theories
- frequency theory (bekesy)
- place theory (Von Helmholtz)
- Travelling wave (George von bekesy)
Frequency theory
- Nerve impulses sent to the brain match the frequency of the sound wave.
- Meaning 30 Hz sound waves should send 30 volleys of nerve impulses.
- Problem: because neurons are limited in their rate of firing, individual impulses fired by groups of neurons cannot produce high enough frequency above 1000Hz, so then how do we hear 4000Hz.
Place Theory
- different frequencies cause different places on basilar membrane to vibrate, like a harp string.
- receptor location corresponds to sound frequency.
- Loudness is coded in terms of both the rate of the stimulus and which specific hair cells are sending messages.
- problem: membrane is not like a harp
who made place theory
(von Helmholtz, 1863)
who made frequency theory
(Bekesy 1957)
at which frequency do which theory work
· At low frequencies, frequency theory holds true, at high frequencies, place theory provides mechanisms for coding the pitch of a sound.
sound localization
- made by Brown and Luck
- The nervous system uses information concerning time and intensity differences of sounds arriving at the two ears to locate the course of the sounds in space.
Travelling wave
- observed that the whole membrane moves
- but peaks at a certain location, depending on frequency
- encodes higher frequencies
types of hearing loss
conduction deafness and nerve deafness
conduction deafness
caused by problems involving the mechanical system that transmits sound waves to the cochlea. Use of a hearing and amplifies the sound entering the ear. May correct conduction deafness.
Nerve deafness
caused by damaged receptors within the inner ear or damage to the auditory nerve. Cannot be helped with a hearing aid.
Gustation
- TASTE
- tongue has small bumps called papillae, which contain taste buds
- taste bud: each is made up of several taste receptor cells
- primary tastes:sweet,sour,salty,bitter,umami
- purpose: determine whether novel foods are edible
Umami
An additional taste sensation that increases the sensitives of other taste qualities
Olfaction
- SMELL
- stimuli: volatile airborne molecules
- attach to olfactory binding proteins in olfactory mucosa
- stimulate cilia on olfactory receptor neurons==> olfactory bulb.
- one pathway goes to olfactory cortex (conscious experience), another to limbic system (memory & emotion)
- difficult to classify odourants into primaries.
• this explains the “asparagus urine”
Olfactory Bulb
A forebrain structure immediately above the nasal cavity, each odour excites only a limited portion of the bulb, odours are then coded in terms of specific areas of the bulb that is excited.
asparagus urine
phenomenon. metabolites of a compound in asparagus are excreted in urine, giving it a distinctive smell. 40% ppl have the gene to smell it tho.
Cutaneous senses
touch/vibration, warmth, cold, and pain
vestibularsense
balance
Proprioception
sensing position of the body and limbs
kinesthesis
sensing movement of the body and limbs
Pain
- minimizes exposure to noxious, aversive stimuli
- not sensory overload
- two kinds, each has unique sensory subsystem:
• first pain
• second pain - affected by non-physical factors, like cultural background
First pain
sharp, brief, highly localized
Second pain
deep, dull, more diffuse
catch trials
no stimulus is presented 50% of the time.
