PSYA01H3 Chapter Notes - Chapter 4: Gustav Fechner, Detection Theory, Visual Acuity
Chapter 4
Sensation and Perception
synesthesia: perceptual experience of one sense that is evoked by another
sensation: simple stimulation of a sense organ
perception: organization, identification and interpretation of a sensation in order to form
a mental representation
transduction: takes place when many sensors in the body convert physical signals
from environment into encoded neural signals sent to the central nervous system
-In the mid 1800’s, Gustav Fechner developed psychophysics: methods measuring
stimulus strength and observer’s sensitivity to it
absolute threshold: minimal intensity needed to just barely detect a stimulus
just noticeable difference (JND): minimal change in a stimulus that can just be
detected
Weber’s Law: the just noticeable difference of a stimulus is a constant proportion
despite variations in intensity
signal detection theory: an observation that the response to a stimulus depends both
on a person’s sensitivity to the stimulus in the presence of noise and on a person’s
decision criterion
sensory adaptation: sensitivity to prolonged stimulation tends to decline over time as
an organism adapts to current conditions
Vision l: How the Eyes and Brain Convert Light Waves to Neural Signals
visual acuity: ability to see fine detail
Physical and Psychological Dimensions of Light Waves
-length: hue/colour
-amplitude: brightness
-purity: richness of colour
Human Eye
-light reflected off a surface passes through cornea which bends it and sends through
pupil
-iris: coloured part around pupil, controls size of pupil
-behind iris: thickness and shape of lens adjust to focus light onto retina (light sensitive
lining at back of eye)
accommodation: process by which the eye maintains a clear image on the retina
myopia: nearsightedness, eyeball too long
hyperopia: farsightedness, eyeball too short
photoreceptor cells: cones: 6 million; detect colour, operate under normal daylight
conditions and allow us to focus on fine details. rods: 120 million; become active under
low-light conditions for night vision
fovea: very center of retina where vision is clearest and there are no rods at all
!--> decreases the sharpness of vision in less light, however looking a little
towards the side of target helps
retina:
!retinal ganglion cell - bipolar cell - photoreceptor cells (cones and rods)
blind spot: location in visual field that produces no sensation on the retina
receptive field: region of the sensory surface that, when stimulated, causes a change
in the firing rate of that neuron
Seeing Colour
-in 1670, Sir Isaac Newton pointed out that colour is not actually IN light, it is actually
our perception of wavelengths from the spectrum of visible light
!shortest: deep purple, then blue, green, yellow, orange, longest: red
-we see a certain colour on a surface because it reflects that wavelength and absorbs
every other one
-additive colour mixing: increasing reflected wavelength. When all visible wavelengths
are present, we see white
-subtractive colour mixing: removes wavelengths, thus absorbing lightwaves we see as
red, blue or yellow. When all wavelengths absorbed, we see black.
S-cones - blue, M-cones - green, L-cones - red
trichromatic colour representation: pattern of responding across the three types of
cones that provide a unique code for each colour
colour-blindness: one, two, or three of the cone types are missing
colour-opponent system: pairs of visual neurons that work in opposition
!red against green, blue against yellow
area V1: part of occipital lobe that contains the primary visual cortex
visual streams project from occipital cortex to visual areas in other parts of the brain
!-ventral (“below”) stream: shape and identity (“what it is”), occipital to lower
temporal lobe areas
!-dosral (“above”) stream: location and motion (“where it is”) up from occipital to
parietal
