Chapter 2 (just vision) Flashcards
Perception
The subjective experience of sensory information after having been subjected to cognitive processing.
Templates
Stored representations of objects enabling object recognition (similar to schema)
-Template matching can only occur (if it occurs at all) after information from the outside world has been encoded in some way by the visual system.
Reversible figures
Gestalt
A figure in which the object perceived depends on what is designated as ‘figure’ and what is designated as ‘background’ (Vase oder Gesichter)
-demonstrates the influence on perception that organising things into figure and ground can have
Laws of perceptional organization
Principles (such as proximity) by which parts of a visual scene can be resolved into different objects
Features
Elements of a scene that can be extracted and then used to build up a perception of the scene as a whole. See also ‘geons
-A variation of template theories that concentrate on simple components of objects instead of the entire object
Pandemonium
A fanciful but appealing conceptual model of a feature extraction process.
Hierarchy of neurons(demons in the example): some only react to visual perceptions (lower levels of visual perception), higher up neurons only react to certain patterns of neurons down the hierarchy, detecting more complex features
Marr’s computational theory
There are several stages to visual perception.
- Primal sketch
- 2.5-D sketch
- 3-D sketch
Primal sketch
First stage in Marr’s model of vision, which results in computation of edges and other details from retinal images.
2.5-D sketch
Second stage in Marr’s model of vision. Aligns details in primal sketch into a viewer-centred representation of the object.
3-D sketch
Third stage in Marr’s model of vision. This is a viewer-independent representation of the object which has achieved perceptual constancy or classification. This 3-D sketch can be compared against previously stored representations, and the object can be recognized
Biedermann’s recognition-by-components approach
based on feature extraction.
- the features are three-dimensional and are referred to as geons. Biederman devised a system using 36 basic geons such as cones, cylinders and blocks that could be used to construct a vast range of objects. The basic principle of Biederman’s theory was that if we can identify the geons that make up an object, then we can recognise that object
geons
Basically features, but
conceived explicitly as
being 3-D features
parallel distributed processing (PDP) approaches
Stimuli are represented in the brain, not by single neurons, but by networks of neurons. An approach
sometimes used to model cognitive processes.
-If the object doesn’t quite match the template,
not all the cells in the network may be activated, but many of them may be. Thus, the system can make a ‘best guess’ at what the object is most likely to be–> leads to learning
Illusions
- “physical” illusions like rainbows
- illusions that arise from basic properties of the perceptual system (grid with points at intersection)
- illusions generated through top-down processes
- -> our knowledge influences our perception
size constancy
The perceived size of objects is adjusted to allow for perceived distance.
sensation
The ‘raw’ sensory input (as compared with ‘perception’).
numena and phenomena
by Kant: numena is the world as it really is; phenomena is our perception of the world; we only know the phenomena
sensory conspicuity
The extent to which aspects of a stimulus (such as colour and luminance) influence how easily it can be registered by the senses.
-relies primarily on bottom-up processes
attention conspicuity
The interaction of aspects of a stimulus (such as colour, luminance, form) with aspects of an individual (such as attention, knowledge, pre-conceptions) that determine how likely a stimulus is to beconsciously perceived.
-relies primarily on top-down processes
LBFS accidents
Looked But Failed to See
-accidents where the driver sensed but not perceived the other car/object
It would thus appear that one explanation for LBFS accidents is that more experienced drivers are placing more reliance on what they already know and this is affecting what they perceive
constructivist approach
Building up our perception of the world from incomplete sensory input. See also ‘perceptual hypotheses
-The constructivist theories thus emphasise a strong
interaction between sensory information moving ‘bottom-up’ and knowledge moving ‘top-down’. The interaction of the two determines what is perceived
perceptual hypotheses
An element of the constructivist approach, in which hypotheses as to the nature of a stimulus object are tested against incoming sensory information.
advantages of top-down knowledge based perception
- sensory input is rather impoverished, and we need to ‘construct’ our perception
- we have limited cognitive capacity
visual masking
Experimental procedure of following a briefly presented stimulus by random visual noise or fragments of other stimuli. Interferes with or interrupts visual processing.
- takes attention away from the original stimulus
- is seen as evidence for the constructivist approach
re-entrant processing
Information flow between brain regions (bidirectional).
masking disrupts the re-entrant processing,
criticism to the constructivist approach
it is often tested in the laboratory where people have very little sensory information and are therefore forced to use their knowledge. This effect might not be as strong in the real world
the Gibsonian view of perception
-functionalist, practical view
“perception for action”
-claims that laboratory studies do not demonstrate how we interact with the world
-moving within the environment and interacting with the environment are crucial aspects of perception
direct perception
Perception without the need for top-down processing.
ventral stream
Perception without the need for top-down processing.
- what system
- sits in the inferotemporal cortex
- associated with the constructivist approach
dorsal stream
A pathway which carries visual information about the spatial location of an object.
- where system
- sits in the parietal cortex
- associated with the Gibsonian way
phenomenological experience
Our conscious experience of the world
interaction of ventral and dorsal stream to form our phenomenological experience
The constructivist ventral stream would seem
to be ideal for building up, and maintaining, our representation of the world, recognising objects as they appear in central vision and generating stored representations of those objects for when we are
looking elsewhere. As long as everything remains unchanged, our perception of the world should be fairly accurate. To maintain that accuracy, however, we need a system that will warn us if some part of the visual world changes. This is one of the functions that the dorsal stream could serve.
this dichotomy of ventral and dorsal stream might be overly simplified
