PSYC1101 Lecture Notes - Lecture 8: Color Vision, Detection Theory, Color Blindness
Binding Problem: How are all distinct sensory components of a stimulus bound into a complete
perception.
Sensation
-Stimulus detection process by which our sense organs respond to and translate characteristics
of environmental stimuli into nerve impulses (transduction) that are sent to the brain.
-Sensory organs/equipment is an adaptation to the environment in which a particular species
lives.
Psychophysics: Studies relations between the physical characteristics of stimuli and sensory
capabilities.
-Absolute Threshold - Lowest intensity at which a stimulus can be detected 50% of the time
-absolute limits of sensitivity - highest and lowest ranges that can be detected
-decision criterion - a standard of how certain one must be that a stimulus is present before
announcing they can detect it (individualised)
-signal detection theory - analyses the factors that influence sensory judgements (eg.
Fatigue, expectation, significance of stimulus etc. - Impacts decision criterion).
-Subliminal stimuli - Weak stimuli that can influence behaviour without having even
registered in conscious awareness.
-Difference Threshold - The smallest difference between two stimuli that people can perceive
50% of the time.
-differences between stimuli - smallest differences between stimuli that can be detected
-Weber’s law - The difference threshold is directly proportional to the magnitude of the
stimulus in question (expressed as a Weber fraction). Pg134 for an example. The smaller
the fraction, the greater the sensitivity to differences.
Sensory adaptation = habituation - Frees senses from the constant/mundane to notice informative
changes in the environ that may be important for wellbeing/survival.
Vision: Light waves
-cones - work in good lighting and are sensitive to fine details and colour. In fovea.
-rods - work in dim lighting and are sensitive to movement/the periphery but not fine detail or
colour. Located in the periphery.
-rods+cones synapse to bipolar cells that synapse to optic nerve.
-no photopigments/photoreceptors in the blind spot.
-visual acuity - ability to see fine detail - determined by rod/cone properties.
-most accuracy if look directly. less fine scale recognition outside of foveal central vision bc of
rods.
-visual transduction - rods+cones translate light waves into nerve impulses through the action of
photopigments. Then changes NT release and thus impulse to bipolar cell and then to optic
nerve, to be passed to visual relay system (thalamus) to visual cortex of the brain.
-dark adaptation - the progressive improvement in brightness sensitivity that occurs over time
under conditions of low illumination.
-Colour vision - difference threshold for light wavelengths allow us to distinguish 7.5 million hue
variations.
-the trichromatic theory
-Metamers - physically different stimuli can appear perceptually identical.
-any colour can be produced by some combination of the wavelengths that correspond to
the spectral colours red, green and blue (the three types of colour receptors in the retina). if
all are activated, pure white perception will result.
-Cons - ppl w red-green colour blindness could still perceive yellow. + afterimages
(opponent process).
-Opponent-process theory
-Each of the 3 cone types responds to 2 different wavelengths.
-Blue-yellow, red-green, black-white (opponent processes).
-dual process
-combines trichromatic and opponent-processes theory.
-trichromatic correct for red, green, blue cone sensitivity
-opponent process occurs by stimuli altering rate of firing so opponent colour is seen (not in
cone sensitivity).
-colour-deficient vision
-normal colour vision = trichromats.
-Dichromat (lose one colour system) or monochromat (black and white only).
-Cones may be spaced wrongly for colour blindness as well.
-Analysis and reconstruction of vision
-Retinotopic mapping leads to topographic mapping (Pg. 143).
-neurons tuning bandwidth - neurons in V1 respond best to a particular orientation+a range
around it.
-These neurons are arranged in columns, collectively termed hyper-columns. Each hyper
column contains the neural machinery to encode all possible orientations within a given region
of space (each neighbouring column responds best to a slightly different orientation).
-Receptor hyper-columns get squeezed to respond to lines in only one location in one
orientation.
-population response average from group of hyper columns that encode a certain aspect of a
stimulus (eg. width or speed) will result in finer resolution.
-Reconstructing a unified holistic perception is made up of organised image into figures and
background. (figure-ground segregation - basis of object recognition)
-Images can be clear or ambiguous.
-More difficult without oriented borders.
-All information is then projected to the visual-associate cortex to be interpreted in accordance
with memories and past knowledge of objects. - allows object recognition and appropriate
response initiation. We use prior knowledge to disambiguate perception.
-things further away take unless space on the retinal image to look smaller.
-linear perspective; parallel lines appear to converge as they extend into the distance. Space
between lines will change linearly as a function of distance.
-Interposition; assume it still exists behind objects in front even if you can't see it. eg. Triangle
covered partly by a circle - assume behind is the rest to make a full triangle.
-relative height; below the horizon objects higher in the visual field appear to be farther away.
as things vary in size between feet and horizon, change in distance. if change across horizon,
probably just change in size. Above horizon objects lower in visual field appear to be farther
away.
-nearer to horizon, further away it probably is.
-Monocular clarity; understanding that light is scattered by the atmosphere. more distant
objects appear fainter, bluer and less distinct (blurry).
-relative size; a comparison of Sie between items without knowing absolute size of either one
assumes smaller are farther away.
-motion parallax; images closer to the observer move faster across the visual field (take up
more space on the retina) than images farther away.
-binocular disparity; differences between two retinal images of the same scene (info from
difference between image on both eyes). Basis for stereopsis - a vivid perception of the
3Dness of the world that is not available with monocular vision.
-Visual perception has a critical period - Blakemore and Cooper. (Only say vertical lines for first
part of life - had good neutrons for vertical but no neutrons left in its brain for horizontal
coding).
Audition: Sound waves
-Sound = Not absolute (sensitised or desensitised based on previous sound level exposure).
-frequency - no. of waves per second (Hz) = perceived pitch
-below 1000Hz and above 1000Hz - 2 processes for coding
-frequency theory of pitch perception - Neve impulses sent t the brain match the frequency of
the sound wave. Con; neurons limited rate of firing means cannot produce high enough
frequencies of firing to mach sound wave frequencies above 1000Hz.
Document Summary
Binding problem: how are all distinct sensory components of a stimulus bound into a complete perception. Stimulus detection process by which our sense organs respond to and translate characteristics. Sensation of environmental stimuli into nerve impulses (transduction) that are sent to the brain. Sensory organs/equipment is an adaptation to the environment in which a particular species lives. Psychophysics: studies relations between the physical characteristics of stimuli and sensory capabilities. Absolute threshold - lowest intensity at which a stimulus can be detected 50% of the time. Absolute limits of sensitivity - highest and lowest ranges that can be detected. Decision criterion - a standard of how certain one must be that a stimulus is present before announcing they can detect it (individualised) Signal detection theory - analyses the factors that in uence sensory judgements (eg. fatigue, expectation, signi cance of stimulus etc. Subliminal stimuli - weak stimuli that can in uence behaviour without having even registered in conscious awareness.
