Overall Research Aims
The investigation of the processes intervening between the
presentation of an object in the world and the emergence of
a visual percept can be separated into three non-interacting
Formation of the optical image on the retina;
Signal transduction and neural transformation in the retina;
Central processing in the brain.
This division of the overall task is possible because retinal
image formation takes place entirely in the realm of optics
and because in the mammal there is no descending pathway to
the retina, which carries out its function in isolation. It
follows that, if adequate knowledge is available about the first
two stages, and if precautions are taken to retain stability
and stationarity between the visual world and the eye, then
the pre-conditions are met for a scientific study of cortical
processing of perception.
Two radically different modes of approach are available. The
"hardware" of the brain can be studied by such means as direct
recording the activity of brain cells and their connections
as well as by the less selective procedures of electro-encephalography
and imaging. Or analytical experiments can be performed to gauge
neural processing from changes in the intact organism -- externally
observed behavior in animals or the reports of the personal
experience of a human observer (psychophysics).
The enormous amount of interaction continuously taking place
within the functioning brain demands specificity in the conditions
of the experiment. To home in on the operation of the first
neural stages of brain processing of visual stimuli, it is necessary
to keep the more global operations of memory, attention and
learning invariant, or, reciprocally, if the specifics of either
memory formation or the plastic changes in learning or attention
are the subject of study, one should use simple and repeatable
Current Experimental Program
The focus is on the perception of spatial and spatio-temporal
relationships in the visual world. Within the sensory modality
of vision, one can distinguish between such attributes
of a seen feature as location, contrast, color, depth, and motion.
That there is universal agreement on the separability of such
properties of a visual sensation -- in subjective personal impressions,
in language, and in animal behavior -- implies that they each
have their own stream of brain processing. In other words, they
are processed in parallel. Anatomical and neurophysiological
studies have born this out. Yet these studies have only very
partially elucidated the channeling of information within the
streams, in part because the neural circuits involved are intricate
and difficult to disentangle by current neurobiological techniques,
and in part because in the absence of an astronomical set of
random probing stimuli, insight from the perceptual experience
still remains the most powerful guide. Models based on mathematical
concept also come to mind as possible tools, and the laboratory
takes their study seriously, specifically as regards the validity
of their fundamental assumptions and the possibility of their
yielding testable propositions.
An experimental program is actively being pursued in which
the sensitivity of human observers to variations in spatial
and temporal parameters of simple visual configurations is examined.
The aim is to accurately describe the ultimate differentiating
capacity of the organism and hence to delineate the operating
characteristics of the neural circuits that sort incoming visual
signals in the cortex. Results reveal quite surprising abilities
to discriminate between stimuli, and serve as benchmarks that
future descriptions of neural circuitry must eventually reach.
In the process, interesting new findings emerge on the interacting
influences of learning and attention on even these early stages
of cortical processing.