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Intro To Perception Notes

Psychology Notes > Intro to Biological and Cognitive Psych (1st year) Notes

This is an extract of our Intro To Perception document, which we sell as part of our Intro to Biological and Cognitive Psych (1st year) Notes collection written by the top tier of Durham University students.

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Light transformation
Receptor processing
Neural processing
Human Eye Anatomy
Retina = covers eye - processes image
Fovea = high visual acuity
Optic disc = has a blind spot
Optical system: Iris, pupil and cornea = focusing
Macular degeneration = weakening of retina in fovea - more blind sports

Spectrum of visible light = 400-700nm
Short λ = High Electromagnetic E
Long λ = Low EE
Length = humans see as colour
Intensity = humans see as brightness
Purity = humans see as saturation
Light adaptation = pupils expand/contract depending on brightness

2) 1ST TRANSFORMATION  cornea, pupil, lens, retina
= Light reflected from an object is transformed  retinal image
Inverted object rep on retina = up/down L/R
Accommodation = focusing an object on retina  ciliary muscles, lens, fovea
Far Point = dstance at which light focuses on retina
Near Point = accom limit - close up
Accom to near targets

Accom to far targets

Tight muscles
Thick, curvy lens
Light bent
Focus point = before fovea
Relaxed muscle
Slim lens Perception
Little light bending
Focus = behind fovea
Myopia = near-sightedness - concave glasses
Hyperopia = far-sightedness - convex glasses

3) 2ND TRANSFORMATION  photo receptors (rods, cones)
Transduction = retinal image is transformed into electrical signals by photo receptors and sent to the

Absolute number
Dark adaptation
Absolute sensitivity
= ability to detect light in darkadapted eye
= detail vision in light adapted eye
Neural convergence
= no. neurons synapse onto a single neuron
Spectral sensitivity
Colour vision 2 types of vision

Rods 120 million / eye
Retinal periphery
Initially slow, but continue to full adaptation

Cones 6 million / eye
Fovea and periphery
Initially rapid, then plateau





Short λ
Scotopic vision

Long λ
Yes (S, M, L cones)
Photopic vision

Purkinje shift = increased sensitivity to short λ in dark adapted eye
Mesopic vision = rod and cone vision together
Neural Convergence = many neurons (rods/cones) synapsed onto 1 neuron (Ganglion cell)
S cones - Short λ - Blue
M cones - Medium λ - Green
L cones - Long λ - Red

4) Electric signal travels through the LAYERS OF THE RETINA

1. Photo receptors

2. Horizontal connectors

3. Bipolar cells

4. Horizontal connectors

5. Ganglion cells Perception

5) Light reaches GANGLION CELLS
On-centre receptive field = excitatory area  more firing when stimulated
Off-centre receptive field = inhibitory area  less firing when stimulated 3 types of Ganglion cells:
 M cells (magnocellular; parasol): input from rods, not colour specific
 P cells (parvocellular; midget): input from L & M cones, colour specific
 K cells (koniocellular): input from S cones, colour specific
Start of Retino-Geniculo-Striate pathway

6) Electrical signal leaves the eye via the OPTIC NERVE (axons of the ganglion cells)  Results in blind spot
Info  retina optic nerve  LGN in thalamus  V1 in occipital lobe

7) Optic nerve reaches OPTIC CHIASM
Nasal axons cross side and combine with temporal axons from opposite eye
 Contralateral rep of visual field after optic chiasm: L visual field in R, R n L
8) LGN axons fan out and form OPTIC RADIATIONS
9) Optic radiations reach V1
 V1 = primary visual cortex = striate cortex
Neurons in V1 are:
Orientation selective
 the less a stimulus matches a feature, the lower the neuron FR
10) V1 projects into V2
As V1, but increased in complexity (including end-stopped cells)

11) Continues with 2 parallel CORTICAL PROCESSING STREAMS
 WHERE  parietal lobe
 Object location
 V3  V5=MT (middle temporal area)

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