Lecture 3 - The Psychology of visual perception

Question 1

What is sensation?

Answer 1

the un-interpreted sensory impressions created by the detection of a stimulus

Question 2

What is perception?

Answer 2

the psychological, cognitive processes of making sense of the sensations

Question 3

What is structuralism?

Answer 3

• the study of the elements of consciousness
• conscious experience (perception) can be broken down into basic sensory elements which can be combined again to describe any human experience
• Wundt = the father of structuralism

Question 4

What is the method of structuralism?

Answer 4

• introspection
• goal = describe elements of perception
• perception = sum of sensory elements

Question 5

Evaluation of structuralism/ introspection?

Answer 5

+ first ‘school of thought’ in psychology
- lacks validity: no measures, purely descriptive
- lacks reliability: observations are not consistent + constant
- lacks objectivity: observations depend on observer, biased

Question 6

Gustav Fechner 1860?

Answer 6

• book = ‘elements of psychophysics’
• basic idea = measuring rather than describing the elements of perception
• looked at:
  1. method of adjustment
  2. method of limits
  3. method of constant stimuli

Question 7

Method of adjustment?

Answer 7

• p’s adjust the intensity of a test light until they are just able to perceive the light

Question 8

Method of limits?

Answer 8

• p’s are presented with trials of increasing/ decreasing light intensity
  can look at a diagram
• result = stimulus is either detected (100%) or not (0%)

Question 9

Method of constant stimuli (used mostly today in labs)?

Answer 9

• same task as the method of limits but:
  -> many more trials per light intensity
  -> randomised light intensity across trials

Question 10

Ernst Weber 1834?

Answer 10

• basic idea:
  -> measuring the difference threshold
• Webers law = the change in a stimulus to discriminate it from another stimulus is a constant ratio of that original stimulus

Question 11

Stanley Stevens 1957?

Answer 11

• basic idea:
  -> subjective magnitude estimation
  -> measuring the relation between stimulus intensity (objective measure) and perceived intensity (subjective experience)
• an increase in the perceived stimulus intensity can be larger (response expansion) or smaller (response compression) than the increase in the measured stimulus intensity

Question 12

Steven’s power function?

Answer 12

P = KS^n
P = perceived intensity
K = constant (scales values to size)
S = stimulus intensity
n = exponent

Question 13

Evaluation of psychophysics?

Answer 13

+ valid, reliable and objective measure (hard data)
- no theoretical account of perception i.e. unclear how we add meaning to our sensations

Question 14

Theoretical accounts of perception - James Gibson 1966?

Answer 14

• ecological theory of perception
• goal = explain how we attach meaning to sensory input
• perception is direct (perception = sensation)
• perception must be investigated in a natural environment
• perception takes place in the optic array
• its directly based on invariant information in the visual field which is extracted by the observers movement
• i.e. as an observer moves, the optic array becomes ambient (the light surrounding the observer changes), but some information remains constant (invariant)

Question 15

Examples of invariant visual information (Gibson 1966)?

Answer 15

1. Optic flow pattern:
   -> The focus point of a driver remains motionless while the rest of the visual field appears to move away from this point
2. Texture gradient:
   -> the elements of a textured ground are denser in the distance
3. Horizon ratio:
   -> the proportion of the object above and below the horizon is constant for objects of the same size standing on the same ground

Question 16

Evaluation of the ecological theory?

Answer 16

+ theoretical account (tries to explain how perception and object recognition work)
+ assumes that perception, offered by the real world is fast, readily available, effortless and always accurate