Perception Flashcards
What is perception for?
Organism is adapt to environment to survive and reproduce
Animals movement regulated by environment
What is perception?
The ability to detect structures and events in surroundings
Indirect process involving construction based on sources of energy
Most animals use light as it provides a wide range of information:
Chemical diffusion cannot pinpoint exact location
Mechanical pressure only gives information about objects in immediate contact
Sound does not Usually signify environmental structure
Sensory modalities
Vision Hearing Touch Smell Taste
What is light?
One form of electromagnetic radiation- propagation of energy though space
Absorption:
Photons collide with particles of matter
Reflection:
Striking an opaque surface (other wavelengths may be absorbed)
Diffraction:
Passes through transparent media
Gibson’S light information
Ambient optic array
Light will converge from all directions
The Eye:
Enables directional sensitivity- can perceive the spatial structure rather than sum total of light
Cones:
Fine detail/colour
Rods:
Movement/coarse detail
Top-down processes:
Use knowledge about the structure of the world to influence perception ‘conceptually driven processes’
Bottom-up processes:
Take info coming into eye and make judgements about nature of visual world solely based on this info ‘data driven processes’
Helmoltz constructivist approach assumptions:
Perception is an active and constructive process
Perception is an end product of the presented stimulus and internal factors (hypotheses expectation and motivations)
As perception is influenced by hypotheses that will sometimes be incorrect it is prone to error
Gregory elaborated top down approach as perception as inference:
Perception is not determined simply by stimulus patterns rather it is a dynamic searching for the best interpretation of the available data, perception involves going beyond the immediately given evidence of senses
Two aspects of vision:
Perceptual constancy
Illusions
Types of constancy:
Size Colour Shape Orientation Location
Perceptual constancy:
Viewing objects under conditions such that their true properties (shape size) are not reflected in the retinal image they project
What does perception require?
Requires sensitivity to at least one form of energy that can provide info about the environment
Visual illusions caused by
Phenomenal phenomena
Geregory identified 4 types of optical illusions:
1) Distortions (Muller Lyer) a perceptual error
2) Ambiguous figures (Rubin’s vase) same input but different interpretations
3) Paradoxical figures (penrose triangle) assumptions about 3D structure
4) Fictions (Kanizsa triangle) perception of an absent form
Evaluation of Gregory’s Theory
Gordon- empiricism
But conceptual understanding seldom destroys illusions, why are we unable to modify our hypotheses in an adaptive way
Commonality in perceptions with idiosyncratic worlds?
Eysenck and Keane Gregory good at explaining illusions rather than perception as a whole
Milner and Goodale: info from primary visual cortex diverges into 2 anatomical streams…
Dorsal- vision for action
Ventral- vision for identification
Which stream do illusions tap?
Ventral stream
Why should the vision for action system be immune to illusions?
Needs to provide accurate info about the world
Haart et al tested whether the dorsal stream was immune to illusory effects by having participants grasp the…
Muller Lyer Figures
Constructivist approaches characterise perception as…
Inferences made on the basis of sparse material
Gibsons theory of direct perception
Ecological approach
Primary function of perception to facilitate interactions between individual and environment
Ambient optical array provides unambiguous info about layout of objects of three main forms:
Optic flow pattern
Texture gradients
Affordances
Optic flow patterns
Further a part is from the pole the faster its apparent movement
Objects gradually move out of the visual field and are replaced by new objects emerging at the pole
Optic flow and driving
Lee- locomotor flow line
Destination point constantly changing
Texture gradients
Occur when a textured surface is viewed at an angle so that the individual elements are packed closer as distance from the observer increases
Provide info about distance and depth
Indicate orientation of surfaces
Why do texture gradients provide invariant info?
They remain constant during movement of observer
Monocular depth cues
Atmospheric perspective
Linear perspective
Occlusion
Light and shade
Affordance
What it can offer
Humphreys and Riddoch neglect
Hemispatial neglect neuropsychological condition where patients fail to respond to items in contralesional visual field
How do percievers pick up this invariant info that is provided by visual world
Gibson: Resonance
Analogous to the workings of a radio
Trouble with illusions
Gibsons theory cannot account for non veridical perceptions brought about by illusory stimuli