Chi Wong   

Deictic codes for the embodiment of cognition

What is the meaning of deictic?

Main Entry: deic=B7tic
Pronunciation: 'dIk-tik also 'dAk-
Function: adjective
Etymology: Greek deiktikos able to show, from deiktos, verbal of deiknynai= to show
Date: 1876
: showing or pointing out directly <the words this, that, and those have= a deictic function>

The word deictic means "pointing" or "showing." It is= an adjective used chiefly to characterize uses of language where a significant part of= the meaning is conveyed through contextual demonstration of some type. These linguistic= deictic devices could be though as being pointers. A pointer is a device that indicates or= reveals something not explicitly representing that thing but by pointing to it. The= usage of pointers might play a crucial representational role in cognition without= themselves being representations of the things represented.

Ballard argue for use of deictic primitives, or pointers to objects in= the world, as a means by which the nervous system exploits external structure, extracting= data with respect to current points of interest, rather than constructing= representations in arbitrary frames. Ballard points out that eye movements are a kind of= deictic device, a kind of pointer. Ballard claims that eye fixations bind variables to deictic= pointers. He present evidence indicating that the spatial context for perception is= provided by deictic pointers such as eye position.

Ballard adopt the basic principle of deictic coding from the field of= computer science where pointers provide a standard technique for the manipulation of complex= data structures. Their primary application of this principle to sensory= processing is in the sequences of fixations and intervening saccades which accompany our visual= world.

The brain is an extreme energy consumer, and there are limits to what the= body may spend for a central system controlling its interaction with the environment.= An obviously efficient way to spend energy is to process only those events that are= absolutely crucial at a given moment, and to use support devices with lower energy demands. It= is not always necessary to process all components of the environment if mechanisms exist= that allow missing components to be rapidly acquired. Taking the example of the eye,= the limited area of highly concentrated photoreceptors and the low convergence to retinal= ganglion cells restrict the energy-consuming processing largely to the fovea. The retinal= periphery only transmit a sketchy overview image to the brain, which requires less energy= for processing. However, the fovea can be rapidly moved by saccades to previously peripheral= objects when they need to be processed with high resolution. This makes it possible to= establish an accurate visual representations of the important components of the= environment despite low acuity peripheral vision.

Ballard hypothesize that foveation may in fact constitute a pointer= mechanism and that saccadic eye movements serve as pointing devices. Saccadic eye movements= make it possible to reduce energy consumption by serving as pointers for cognitive= operations. By using pointers, it reduces the computational load.

Ballard focuses on the 1/3 second time scale, which is the shortest time= scale at which a body movements such as eye movements can be observed. The time scale= defines a special level of abstraction, which is call the embodiment level. At this level, the= appropriate model of computation is very different from those that might used at shorter= or longer time scales. Computation at his level governs the rapid deployment of the= body's sensors and effectors to bind variables in behavioral programs. It is embodied= because it involves a distinctive computational primitive, the "physical act," such as= an eye movement.