PSYA01H3 Chapter Notes -Cerebral Cortex, Myocyte, Cochlea

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6 Nov 2011
PSY – Chap 5 Notes: Sensation
Sensory Processing
Experience is distinguished between sensation and perception
oSensation: the detection of simple stimuli (bright, warm)
oPerception: detection of objects, their location, movement, etc.
Seeing the colour red is sensation; seeing a red apple is perception
Our sensory mechanisms: visual, auditory, gustatory, olfactory, somatosensory
Transduction: sense organs convert energy from environmental events into neural
activity. Transduction is received by Receptor cells- which release neurotransmitters that
stimulate other neurons and alter the rate of firing of their axons.
The body can discriminate between different stimuli by using code:
oAnatomical coding: different features are coded by the activity of different
oTemporal coding: different features are coded by the neural pattern of activity.
Rate of firing tells how intense a stimulus is.
Psychophysics: “physics of the mind.” Studies the relationship between physical stimuli
and perceptual experience
Just Noticeable Difference (jnd): smallest difference between 2 similar stimuli that can be
oThe energy necessary to produce a jnd increases with the magnitude of the stimuli
Signal Detection Theory: every stimulus requires distinction between Signal and Noise
(background stimuli + random nervous system activity)
oAlso emphasizes that sensory experience involves factors other than the activity
of the sensory systems- such as motivation and experiences
Threshold: the line between not perceiving and perceiving.
Difference threshold: the jnd can be called a difference threshold- the minimal detectable
difference between 2 stimuli
Absolute threshold: the minimum value of a stimulus that can be detected- from no
stimulus at all.
Response bias: tendency to say “yes” or “no” when you are not sure whether you
detected the stimulus
Receiver Operating Characteristic Curve (ROC curve): a graph of hits and false alarms of
participants under different motivational conditions. Indicates people’s ability to detect a
particular stimulus.
In order to perceive an image clearly, our eyes are constantly making small movements
Cornea: transparent tissue covering the front of the eye
Sclera: the tough outer layer of the eye, the “white”
Iris: the pigmented muscle of the eye that controls the size of the pupil
Lens: the transparent organ situated behind the iris, helps focus an image on the retina
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Retina: tissue at the back on the eye ball, contains the photoreceptors and associated
Accommodation: changes in the thickness of the lens of the eye that focus an image on
the retina
Photoreceptor: neuron that transduce light into neural activity (cone or rod)
Optic disc: all the axons leave the eye at this point and join the optic nerve, which travels
to the brain
Bipolar cell: a neuron in the retina that receives info from photoreceptors and passes it on
to the ganglion cells
Ganglion cell: neuron in the retina, receives info from bipolar cells, its axons proceed
thru the optic nerve to the brain
Rod: sensitive to light but cannot detect colour
Cone: responsible for day time and colour vision
Fovea: small pit in the centre of the retina (contains densely packed cones). Responsible
for our most acute vision
Photopigment: a complex molecule found in photoreceptors, when struck by light, it
splits and stimulates the membrane of the photoreceptor in which it resides. Rhodopsin is
the photopigment in rods.
There are 3 types of purposive movements:
oVergence: 2 syes cooperate to look at the same thing
oSaccadic: rapidly scanning a visual scene
oPursuit: ability to maintain/follow a moving object
Vision is a Synthetic Sensory Modality: it synthesizes (puts together) rather than analyzes
(takes apart). When 2 colours mix, we see the intermediate- not the 2 separate
Cones in the human eye contain 3 types of photopigments: Blue, Green, Red
oThere are more green and red, less blue
Trichromatic Theory: the theory that color vision is accomplished by 3 types of
photoreceptors, each of which is maximally sensitive to a different wavelength of light
The ganglion cells are yellow/blue and red/green. How does the brain know whether the
light is green/red, if the 2 colours are located on the same cell?
oThe Opponent Process: the colours are represented by the rate of firing (fast=red ,
slow=green)(fast=yellow , slow=green)
Forms of color blindness:
oProtanopia: defective red cones
oDeuteranopia: defective green cones
oTritanopia: lack of blue cones
Ossicle: the 3 bones in the ear: hammer, anvil, stirrup)
Cochlea: snail shaped chamber where auditory transduction takes place
Basilar membrane: contains auditory receptor cells. Within the cochlea
The oval window and round window are both holes in the cochlea with membranes. In
the oval window, the stirrup presses against the membrane and transmits vibrations to the
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