Part 1 referenced the source of my interest in embodied cognition to conversations with Dr. Carl Hillier, introduced the distinctions between egocentric and allocentric spatial projection, and their unification in the Brock String technique for vision therapy. Consider a couple of other examples. A well-known procedure in vision therapy, space matching, asks the patient to judge when the space between object A and object B is equal to the space between object B and object C, and can be done readily with three chairs in three dimensional space. It can also be done by estimating space between points on a chalkboard, and confirming one’s estimate with a ruler. That is an example of a purely allocentric judgement. Contrast this with the space fixator procedure introduced by Dr. Bob Sanet and elaborated by Dr. Tanner Gates, which is a visually guided action using egocentric spatial frames of reference.
As noted in the book I referenced in part 1, egocentric parameters are cued by the proprioceptive system, particularly by kinesthetic sensors in muscles, tendons, and joints, and by efference copy monitoring the motor command. Efference copy is integral to embodied cognition, and believed to play a key role in adaptive changes seen in strabismus as evidenced by the experiments in this article on visually guided action.
Back to Brock, and the notion I blogged about previously that his three beads conveniently affords the therapy setup to parse visual space into three principal regions now commonly referenced in neuropsychology: personal, peripersonal, and extrapersonal.
This takes on great potential significance in acquired brain injury, with evidence that spatial hemineglect may exist in one region of space and not others. In other words, a patient may show left neglect only in near space, only in far space, or both. For example, a patient may exhibit neglect in line bisection peripersonal space with a dowel stick, but not when using a laser pointer to perform a line bisection task as an overhead projection across the room. Further, many of the tests for neglect such as line bisection or clock drawing only reveal the more extreme cases, since they probe only two dimensional rather than three dimensional space.
I therefore postulated, in a book chapter co-authored with Dr. Sanet on Spatial Vision in ABI, that the Brock String opens up new vistas in exploring these three relative regions of three dimensional visual space.
Sue Barry, in an insightful article reprinted in Optometry & Visual Performance, imparts the wisdom of Dr. Brock regarding visual posture and therapy procedures. I am hypothesizing that by providing a continuum of physiological diplopia from personal space through extrapersonal space, Dr. Brock anticipated the power of embodied cognition in combating spatial hemineglect. My experience has been that when a patient with ABI does not have strabismus or suppression, physiological diplopia serves as a strong stimulus to counter neglect, inattention, and extinction. This is because the string is presented along the midline as a single object, and registers in both hemispheres simultaneously.
Lastly, the book we’ve been referencing has an excellent chapter by Paul Cisek that provides a framework for embodied behavior. In a subsequent paper co-authored by Dr. Cisek in Annual Review of Neuroscience (2010) he notes:
Theories of embodied cognition have suggested, following Piaget,that cognitive abilities may have evolved within the context of ancestral abilities for interacting with the world. Our ability to think about the world results from the internalization of the processes of predicting the consequences of actions. As the sensorimotor control system gradually evolved, it began to predict increasingly abstract consequences of behavior. This eventually allowed the mental rehearsal of entire sequences of acts and evaluation of their potential outcomes, without overt motor activity. This hypothesis is consistent with the close relationship between mental imagery and the systems for motor preparation and potentially explains how an organism may go beyond merely reacting to properties of the immediate environment and act in a goal-directed manner. Here’s a delightful video lecture by Dr. Cisek giving embodied cognition its proper accord as a mediator between input and output functions of the brain and body.