Unit 3, Topic 2 - Visual perception Flashcards
Visual perception process
Reception, transduction, transmission, selection, organisation and development
Visual reception
Light enters the cornea, passes through the pupil, and is focused on the retina by the lens. Receptors in the eye detect and respond to the visible light spectrum pf electromagnetic radiation.
Visual transduction
Photoreceptors (rod cells-black/white, and cone cells-colour) convert electromagnetic energy into electrochemical nerve impulses. Light is transduced in receptive fields, which are areas of the visual field received by particular clusters of photoreceptors which are connected to a single neuron.
Visual transmission
Visual information is sent to the visual cortex (occipital lobe) along the optic nerve, via the thalamus.
Visual selection
Feature detector neurons in the primary visual cortex select which visual stimuli we pay attention to. They activate when certain attributes are present, breaking down the key parts of the image.
Biological influences on visual perception
Physiological makeup: damage or impairment of visual structures (e.g. myopia/hyperopia)
Ageing: associated with poorer vision (e.g. presbyopia, cataracts)
Genetics: many genetic disorders are inherited (e.g. colour-blindness)
Visual organisation and interpretation
Images are organised and given meaning through the use of visual perception principles (Gestalt, dept cues, visual constancies)
Perceptual set
An individual’s predisposition to view stimulus in a certain way based on past experiences, context, motivation, and emotional state.
Gestalt principles
Figure-ground organisation, closure, similarity, proximity
Binocular depth cues
- Retinal disparity (disparity between right and left retinal images)
- Convergence (eye muscles turning inwards for closer obejcts)
Monocular depth cues
- Accommodation (muscle tension to focus lens)
- Pictorial depth cues (linear perspective, interposition, height in plane, texture gradients, relative size, light and shadow)
Hudson 1960
Concluded that 3D interpretation of images was a cultural skill (showed images with pictorial depth cues to people from a village in South Africa vs Caucasians)
Deregowski 1972
Concluded that many non-Western people lack pictorial depth perception and prefer split drawings to perspective drawings, likely due to limited experience with depth cues.
Deregowski, Muldrow & Muldrow 1972
Concluded that perception was mostly based on the person’s familiarity with the image depicted, although unfamiliar images could be recognised with effort.
Muller-Lyer
Two vertical lines with different ends. The one with the feathered tail is perceived as longer than the one with arrow heads. ‘Carpentered world hypothesis’ attributes this to use of linear perspective depth cue. ‘Perceptual compromise theory’ attributes this to the gestalt principle of closure.
Ames room
Causes people to perceive false differences in object size. Works due to trapezoidal shape of room (rectangle expected due to perceptual set), viewing of the room with one eye which prevents use of binocular depth cues, and the manipulation of pictorial depth cues.
Ponzo visual illusions
Two horizontal lines between converging vertical lines. The upper horizontal line is perceived as longer due to the depth dues of linear perspective and height in plane.
Ambiguous figures
Ambiguous figures can be interpreted in multiple ways because they induce multi-stable interpretation, often by manipulating gestalt principles.
Impossible figures
Impossible figures are 2D images that generate a 3D perception which would not occur in reality. They manipulate pictorial depth cues so that we perceive apparent depth where it cannot actually exist.
