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Two Theories of Perception and affordances

October 16, 2007

I found a paper about the differences of constructive and ecological aspects of perception and their interrelations, that was much in line with the theoretical affordance concept how i understand it, consisting of matching of two kind of aspects coming from the environment and from internal goal-directed processing.

These issues also make me think of our discussion with Mauri Kaippainen: he suggested that in Neisser framework the exploration is sort of unconscious scanning that does not involve so much goal-directed mental construction in advance (seems like ecological framework to me), while i thought that after a while this scanning as a spiral activity will be more and more conscious (seems like constructive framework to me). Also i suggested that sometimes we start exploration by shifting some internal imagination to the external environment, actualizing some aspects there – this again seems like constructive perception to me, where schemata must be internally processed in order to perceive something in the environment.

Joel Norman:Two Visual Systems and Two Theories of Perception: An Attempt to Reconcile the Constructivist and Ecological Approaches

Norman, J. (2002). Two Visual Systems and Two Theories of Perception: An Attempt to Reconcile the Constructivist and Ecological Approaches
. Behavioral and Brain Sciences (2002), 25:1:73-96 Cambridge University Press.

According to Joel Norman (2000) the constructivist and ecological theories of perception differ, however, he claims that there is certain continuum rather than dichotomy between approaches. Both approaches to perception, the ecological and the constructivist, are valid descriptions of perception, but of different aspects of perception.

Comparison of two theories to perception:

1. Mental processes to pick up information or not
The constructivists see the stimulation reaching our senses as inherently insufficient necessitating an “intelligent” perceptual system that relies on inferential types of mechanisms to overcome this inherent equivocality of stimulation.
The ecologically oriented theorists argue that the information in the ambient environment suffices and is not equivocal and thus no “mental processes” are needed to enable the pick up of the relevant information.

2. Direct or indirect perception
The constructivists see perception as multistage with mediational processes intervening between stimulation and percept, i.e., perception is indirect.
The ecological theorists see perception as a single-stage process, i.e., it is direct and immediate.

3. Relying on stored information
For the constructivists, memory, stored schemata, and past experience play an important role in perception.
The ecologically oriented approach sees no role for memory and related phenomena in perception.

4. Process versus stimulation
The constructivists excel at analyzing the processes and mechanisms underlying perception.
The ecological approach excels at the analysis of the stimulation reaching the observer.

Milner and Goodale (1995): the ventral stream transforms visual information into an exocentric (also labeled “allocentric”) framework allowing the perception of the object as it relates to the visual world. The dorsal system, on the other hand, transforms visual information into an egocentric framework allowing the actor to grasp or otherwise bodily manipulate the object.

Norman (2000) suggests that if it is true that the two systems function independently and that the dorsal system functions can be carried out with little or no conscious awareness, it is possible that the two systems will be capable of simultaneously processing two different sources of visual information with very little interference.

The primary function of the ventral system is the recognition and identification of the visual input. Recognition and identification must depend on some comparison with some stored representation. In contrast, the primary function of the dorsal system is analysis of the visual input in order to allow visually guided behavior vis-à-vis the environment and objects in it (e.g., pointing, reaching, grasping, walking towards or through, climbing, etc.).

The ventral system is superior at seeing fine details, while the dorsal system is better at seeing motion.

The ventral system is the memory-based system, utilizing stored representations to recognize and identify objects and events. In contrast the dorsal system appears not to have a long-term storage of information, but only very short-term storage allowing the execution of the motor behavior in question.

The dorsal system is the faster.
We are much more conscious of ventral system functioning and hardly conscious of dorsal system functioning.

Ventral system functions aim at recognizing and identifying the object and for this purpose all that is needed is object-centered information. In contrast, the dorsal system must perform some action on, or in relation to, the object, such as grasping it. For this purpose the dorsal system must utilize egocentric frame of reference. In order to be able to pick up the object the dorsal system must utilize absolute metrics, while functions of the ventral system only require relative metrics.

Broader theory of perception is based on the accumulating research findings that point to the existence of two visual systems, the dorsal and the ventral. It was suggested that the ecological approach broadly parallels the functions of the dorsal system, and the constructivist approach broadly parallels that of the ventral system. These two visual systems deal with different aspects of perception. The dorsal system deals mainly with the utilization of visual information for the guidance of behavior in one’s environment. The ventral system deals mainly with the utilization of visual information for “knowing” one’s environment, i.e., identifying and recognizing items previously encountered and storing new visual information for later encounters. But it should be stressed that both systems overlap in the functions they perform.

This last thing is interesting, if to think of the role of perception in determining affordances from the environment in one hand, and affordances of the anticipated activity in another hand, which must be coupled.

Iaccoboni’s studies about mirror neuron function divergence seem to support Norman’s assumptions.

Iaccoboni: canonical neurons seem to be coding the affordance of an object, the pragmatic aspect of how-to-grab-that-thing, rather than its semantic content; mirror neurons do not fire at the sight of an object but will fire at the sight of a whole action. Mirror neurons have auditory access and they enable a multimodal representation of action that is not linked to
the visual channel only.

Ecological approach
Dorsal system: utilization of visual information for the guidance of behavior in one’s environment
– seeing motion
– utilize egocentric frame of reference (i grasp an apple)
Canonical neurons: seem to be coding the affordance of an object, the pragmatic aspect of how-to-grab-that-thing, rather than its semantic content

Constructivist approach
Ventral system:utilization of visual information for “knowing” one’s environment, i.e., identifying and recognizing items previously encountered and storing new visual information for later encounters
– seeing fine details
– recognition and identification of the visual input
Mirror neurons: fire at the sight of a whole action

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One comment

  1. [...] here to read Der Beitrag wurde am Tuesday, den 16. October 2007 um 14:34 Uhr veröffentlicht und [...]



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