Perception and visual cognition
- Created by: Philosophy Emma
- Created on: 30-11-19 17:03
Psychophysics
Invented by Weber and Fechner
One way to measure perception
We try to relate a precisely defined physical stimulus with a precisely measured behavioural response
Light
the agency that causes a visual sensation when it falls on the retina of the eye … it forms a narrow section of the electromagnetic spectrum
Electromagnetic radiation
· waves of energy that are caused by the acceleration of charged particles.
Absolute threshold
the smallest amount of stimulus energy necessary for an observer to detect a stimulus
Method of constant stimuli
Technique of measuring threshold
- Very slow
- No account of observer “decision criterion”, saying yes or no when you haven’t/have seen the flash
Signal detection theory
Technique for measuring threholds
- False alarm rate to account for the decision criterion
Just noticeable difference
- The smallest difference between two stimuli that a person can detect
Sensory adaption
reduces sensitivity; can’t see stars in the daytime, can’t hear very well after concerts
Strong, persistent stimulation decreases sensitivity
Retinal stabilisation
stabilised images fade rapidly
Retinal adaption
if an image is stabilized on the retina it fades, normally our eyes are constantly in motion to prevent this, which serves to reduce visual clutter and concentrate on changes
Cornea
The first place light hits
is perfectly transparent, the skin over the eyes
Amplitude of accommodation
he ability to focus on objects very close or very far away
Photoreceptors
(which consist of rods and cones) detect light and turn light into electricity
This process is called phototransduction
Duplex theory
Rods neural substrate for night vision (scotopic), cones are neural substrate for day vision (photopic)
Soundwaves
Soundwaves are mechanical motions in a fluid medium
We talk about frequency rather than wavelength
Frequency is associated with pitch
We talk about this in cycles per second or herz
Amplitude of the soundwaves determine the intensity, loudness
As the compressions of the waves change, we perceive it as change in volume
Theory of audition
frequency is encoded according to position on the basilar membrane; high near the tip of the cochlear spiral and low on the near centre
Olfactory epithelium
Molecules carried in the air stimulate specific odour receptors in the olfactory epithelium
Achromatopsia
true colour blindness
Subtractive colours
· Mixing paints
· Looking through coloured filters
Additive colours
· Mixing coloured lights
· Television
· Makes the colours lighter
· Pointillist painting
Trichromacy
Young-Helmholtz theory
Three physiological features that underlie our colour vision
Three types of cone photoreceptor: long-, medium-, short-wavelength-preferring
Problems with the theory:
· Complementary colours: Have you ever seen a reddish green? Or a yellowish blue?
· Simultaneous colour contrast: surrounds induce colours
· Negative after images: a red stimulus gives a green afterimage
The theory doesn’t explain all vision phenomena so we have to adjust it
Opponent-process theory
L, M, S cone outputs are recoded into six primaries: red, green, blue, yellow, black, white
Primaries are combined in antagonistic pairs: red-green, blue-yellow, black-white
Some people have argued that it is possible to see reddish-greens and yellowish-blues
Synaesthesia
A merging of the senses
Experiencing unusual perceptions while going about their everyday lives
Can be triggered by sound, taste, smell, touch, letters, numbers, words, music
Affects over 4 % of the population
95 % get colour sensations
Thought to be happen either because of un-pruned neural connections or reduced neural inhibition
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