Cognition- Perception And Attention Flashcards
What is perception?
The process by which we make sense of our surroundings by interpreting the information from our sense organs
Or- the subjective conscious experience of the outside world
- the act of giving meaning to a detected sensation
Subjective experience
What kind of information?
A stimulus is a detectable input from the environment
Light vision
Sound hearing
Chemicals- taste and smell
Pressure,temperature,pain-sense of touch
Orientation, balance- kinesthetic senses
Visual perception- basics
Perceptual constancies
Depth perception
Perceptual organisation
Perceptual constancies
-Central to perception- we use environmental cues to perceive the world
-Shape constancy
An object is perceived as having the same shape when viewed at different angles (even though the retinal image changes depending on the angle, eg- a door open Vs ajar)
-Size constancy
The size of an object is perceived to be constant regardless of how close or far away it is
-Lightness constancy
An objects lightness remains constant regardless of varying amounts of illumination
Spectrum of electromagnetic energy
Field of vision
Light bounces - we see colour
Only see a small part of section but its all we need
We have technology to see
Drivien by evolution only need to see basics of what we need to survive
Depth perception
Objects are 3 Dimensional and have depth, but the retinal image created is only 2 dimensional
Deapth perception is concerned with the cues we use to perceive a 3d world from 2d images
Some cues help us
- binoculars cues (provide depth information when viewing a scene with both eyes)
- monocular cues (provide depth information when viewing from one eye)
- motion cues
Binoculars cues - retinal disparity
- each of our eyes sees the world from a slightly different angle( both eyes offset by about 6cm)
- disparity between images gives cue to distance- the images combine to form a 3-d scene
-Disparity is large for objects close up - disparity is small for objects at a distance
Binoculars cues- convergence
-Refers to amount of rotation our eyes have to do in order to focus on an object
-Angle of convergence is smaller for distant objects
- muscles less stressed when focusing on a distant object
- your brain interprets these muscular movements as indications of distance from you
- sends signals to brain
Monocular cues
Occlusion(or interposition)- when one object partially blocks our view of another, we perceive it as closer
Texture gradients- equally spaced elements are more closely packed as distance increases
Linear perspectives- parallel lines converge as they recede into the distance
Retinal image size- the more distant the object, the smaller the retinal image
Shading- the pattern of light and shade varies across surfaces
Haze (atmospheric perspective) - atmospheric scattering of light means distant objects appear fuzzier
Motion cues
Motion Parallax- closer objects appear to travel across faster than distant objects
Optic flow objects at a distance appear in the centre then move to the side as you approach it eg- road sign
Perceptual organisation
Gestalt laws of grouping
- according to gestalt psychology, humans have a tendency to see patterns rather than random arrangements
Gestalt laws of grouping
Proximity principle- objects near each other tend to be processed as a unit
Similarity principle- objects similar are processed as a unit
Continuity principle- tend to group stimuli into forms that follow continuous lines or patterns
Closure principle- we see complete rather than incomplete figures because we tend to ‘fill the gaps
Perceptual illusions
Perception is constructive process ( information is put together)
When integration fails we experience perception illusions
Ebbinghaus Tichtener circles- which centre is bigger?
Necker cube- where is red dot coming from?
Muller-lyer- two separate lines with arrows in different directions appear to be different length
Penrose stairs- ascending or descending but getting nowhere
Patten recognition
- concerned with how we recognise a particular form for what it is (eg letter A)
Two part processing involving - perceptual processes
- recognition processes
Two major theories
- template matching theory
- Feature detection theory
Template matching theory
- proposal that the visual system recognises objects by matching the neural representation of the image with a stored representation of the same shape in the brain
But
Variations (eg size font position orientation)
Huge number of templates
Time to search it all?
Feature detection theory
All stimuli can be broken down into individual parts (features),
Each of which is analysed by a specific feature detector eg letter a = / -
Hubel and Wiesel used single- cell recording techniques with animals (1963,1968,19
Object perception is complex
Initial object recognition can occur very quickly (150 ms) but the Brain continues to process information
Object recognition should be seen as a conversation among many parts of the brain
Perception disorders- Agnosia
- loss of ability to recognise objects, faces, voices or places
- usually associated with brain injury (strokes, head trauma, or encephalitis can cause lesions)
- only affects a single modality, visual auditory or tactile
- only focusing on common examples of visual Agnosia in this lecture
Visual agnosia
-Problems recognising visual objects
- common forms
Apperceptive visual agnosia
Associative visual agnosia
Prosopagnosia (face blindness)
Apperceptive visual agnosia
Difficulty recognising objects
Patients unable to name an object and not able to draw or copy a picture of an object. Can use vision to navigate the environment. Knowledge of what the object is used for remains In tact. They can still recognise and use an object when they are allowed to touch it.
Recognise object through other senses
Associative visual agnosia
Inability to recall information associated with an object
- patients unable to name an object but can copy it. Patients able to draw a picture of an object, they can still recognize and use object when they are allowed to touch it
Use other senses like smell
