Lecture 3 & 4 Flashcards
Sensation
Un-interpreted sensory impressions created by the direction of a stimulus
Perception
The psychological processes of making sense of a sensation
What is structuralism?
The study of the elements of consciousness. Conscious exprerience can be broken down into basic elements which can be combined to describe all human experiences,
What is the method and aim of structuralism.
Method: introspection Validate perception (no measures, descriptive), reliability (observations are inconsistent) and objectivity (observation depend on observer)
psychrophysics
Measure the absolute (perception) threshold
Basic ideas that measure the absolute perception threshold
Method of adjustment
Method of limits
Methods of constant stimuli
Methods of stimuli intensity.
Method of adjustment
Participants adjust the intensity of a test light until they are able to perceive the light
Method of limits
participants presented with trials of increasing/decreasing light intensity
Method of constant stimuli
Similar to methods of limits, but more trials per light intensity, randomised light intensity across trials
Method of stimuli intensity
Percentage of yes answers are plotted as a function of stimulus intensity.
Ernst Weber (psychrophysics)
Measuring the different threshold, the minimum intensity difference to discriminate two stimuli.
Webers law
The change in the stimulus to discriminate it from another stimulus is a constant ratio of that original stimulus. The stronger the stimuli the greater the change needed for it to be detected.
Stanley stevens (psychrophysics)
Subjective magnitude estimation- measure the relation between stimulus intensity and perceived intensity. An increase in the perceived stimulus intensity can be larger or smaller than the increase in the measured stimulus intensity
Theoretical accounts of perception - ecological theory. James Gibson
Ecological theory of perception.
Describe perception (ecological theory)
Perception takes place in the optic array and is directly based on invariant information in the visual field which is extracted by the observers movement,
Examples of invariant visual information
Optic flow pattern:
The focus point of a driver remains motionless while the rest of the visual field moves away from this point
Ecological theory of perception
Aim of explaining how we attach meaning to sensory input.
Theoretical account tries to explain how perception recognition works.
What are the bottom up accounts of perception.
Structuralism, psychrophysics and ecological theory. They are all stimulus guided perception and information is gathered by the sensory receptors to determine perception completely.
Vertical horizontal illusion
Bisecting lines are perceived as being longer than biseceted (uninterrupted) lines
Jastrow illusion
Longer radii makes objects appear shorter
Irradiation illusion
Light areas appear larger than dark areas
Figure ambiguity
The retinal image will perceive different objects, focus on different aspects reveals different images.
Feature ambiguity
Image could be seen as two different things (rabbit or duck)
Depth ambiguity
Cubes- 3D perception makes it difficult to distinguish the front
Erroneous perception with visual illusions
What we perceive is not always what is represented on the retina
Equivocal perception wit ambiguous figures
We perceive different objects from the same retina image
Moon illusion
Moon appears larger when it is close to the horizon
Waterfall illusion
After observation of motion in one direction stationary objects appear to move in the opposite direction
Wagon wheel effect
A moving wheel appears to be still/move slowly/move in opposite direction upon rotation
The inverse projection problem
A 3D object is represented on a 2D retinal surface. So the real image cannot be derived due to superimposed objects or untypical angles.
What do top down vision theories account for?
Perception being an interaction between sensation and cognition, including stored object knowledge, personal expectation and motivation.
Richard Gregory: constructive theory of perception
Perception is indirect and a construction of hypothesis testing .
Explains how we attach meaning to sensory input.
Does not explain how illusions persist even when the perception is known.
Gestalt theories
Explained how we attach meaning to sensory input.
Gestalt account
Two light flashes in an alternating fashion create movement,
A whole object is achieved by perceptual organisation - grouping and segmentation.
Proximity
Elements that are close together are grouped together
Similarity
Elements that look similar are grouped together
Common fate
Elements that appear to move together are grouped together
Good continuation
Elements that continue are grouped together
Relative size
Elements that are smaller than a surrounding area are grouped
Law of Pragnanz (Gestalt)
Of several geometrically possible organisations the one that will occur is the one that is the most simple
Describe top down accounts of visual perception
Perception is an interaction between sensation and cognition. Information flow is direct from the brain to the stimulus. Information gathered by the sensory receptors is interpreted in line with the observers knowledge, goals and expectations.
Constructive theory of perception (Gregory)
SUMMARISED
Perception is indirect based on hypothesis testing. Perception is an effort and can be ambiguous, could explain perceptual failure. This cannot explain why perceptual failure persists once it is cognitively understood
Gestalt psychology
SUMMARISED
Perception is based on eprceptual organisation (grouping, segmentation) and follows the law of pragnanz.
