Visual Perception
There are three types of receptors (cones) in the eye, tuned for red (long wavelength), green (medium wavelength), and blue (long wavelength). These receptors are interconnected, and can feedback to each other, starting in the eye itself. In the brain there are at least two stages to the construction of a color image, before the main processes of interpretation and meaning. The first stage involves the perception of the intensity of a wavelength band ( V1 cells). The result of this is a grayscale view of the world, which shifts continually depending on the incident light. This stage is usually not consciously perceived. The second stage involves the comparison and contrast of several different wavebands, and produces the experience of color ( V4 cells). The color perceived depends on both the local and global variation over the field of view. [AM]
The perception of continuous motions (in the M system) is achieved at a rate of roughly 24 frames per second. This may be related to basic functions of perception in the brain, e.g. compare with the beta waves of normal consciousness (13-20 Hz), and the gamma waves of synchronized neural activity. [SFF] Depth perception is related to motion perception. [AM]
Nearly half the cerebral cortex is given over to the processing and interpretation of sight. This is the addition of meaning to the images that have been processed by the V regions. [AM]
Perception is based on change, when things don't change they eventually become imperceptible. Moreover perception is relative and relational. In a completely red room, after a period everything will look grey. [SFF] Stepping from a green lighted room into the outdoors, everything appears tinged with red [AHM].
That the world-image of the blind, based on touch, sound, and
smell, bears no inherent relationship to that of the sighted, which
is integrated by visual images, has been shown by the cases of
adults who have their physical sight restored after a long period
of blindness. Although no longer physically blind they
remain mentally blind. Although the physical structures may be
operative, they still need to learn to understand, to create meaning
out of their raw perceptions. The sighted do this in a very different
way than the blind, being able to see many objects at the same time,
to have an awareness of space. The blind have a primary awareness
of time, and only know space through time. E.g. they can only
measure the length of a walk by the time taken, while the sighted
can stand at one end and seeing the other, judge the distance. [AM]
The newly sighted person has to go through all the development
that the infant and child go through, to learn to integrate their
perceptions, top build libraries of images, to construct a whole
new world. This involves as well construction of a whole new self,
and the letting go of, or death of the old non-visual self. This
process can be very traumatic, essentially asking the person to
return to the helplessness of the infant, to wipe out years of
learning and adaption, and to form a whole new self. (This death
and rebirth process has also be experienced by deaf people who
regain their hearing) It appears that sight can not simply be
integrated into the other senses, but allows, or demands, a whole
new way of being, new habits and behaviors. One of these is the
conscious act of looking, as opposed to the passive act of seeing,
to project the awareness and attention out into the world of image
in order to understand and make sense of it. [AM]
The depth of effort and difficulty with which these changes occur
most clearly demonstrates the extent to which we create "our world"
out of our perceptions, and that this is a process of creating our
"self" as well. When the deaf learn to hear they not only create a
new self, but enter a new culture, as the deaf through sign language
can form a world of their own, in a way that the blind generally do
not. [AM]
Learning to see as an adult is even more difficult than the task of
the infant, as they are simply creating something from scratch, while
the newly sighted are almost literally going through a psychological
death and rebirth. It is also more difficult because the world of an
adult is so much more complex than that of the infant or young child.
The infant does not have to try to make sense out of the kaleidoscope
of color on the shelves at the grocery store. This is also done at
a stage when the brain is older, less flexible, and probably involves
massive rewiring of the cortex. It is known that when one sense is
lost, the other senses are enhanced, which includes physical expansion
of the portions of the cerebral cortex
that are used to process those senses. This may come at the expense
of areas the would previously have supported the sense that has been
lost. Any confidence that one has developed as a blind person is
gone in the swirling confusion of new sight. In particular the sense
of distance and depth is not innate, and the
stability of perception that is so ingrained takes a long time
to develop. This means that the person may be aware of single images,
or portions of images, but the integration into dynamic objects is
learned through long effort. On the other hand recognition of color
and motion seem to be innate, perhaps being performed at a lower
level center in the brain. [AM]
It seems that what we find to be unstable or
chaotic in our perceptions is relative. With time and effort we learn
to handle and interpret increasing volumes of information (probably
through processes of generalization, the
formation of categories etc.), or to handle new types of information.
This can be clearly experienced by attending lectures where the
material is either familiar or not. When it is not, much more effort
is required, and usually much less understanding is garnered. Working
in a foreign language may have the same effect, finally tending to
put one completely to sleep, when the effort is to intense or extended.
This sort of fatigue may also be experienced by the newly sighted when
learning to understand their new perceptions. The creation of
stability out of chaos, is also effected by
filtering the incoming perceptions, reducing them to the few key
components that are significant and require conscious attention. [AHM]
In persons who have lost the ability to consciously see (or
experience one of the other senses) due to problems in processing
areas of the brain, rather than the eyes, there may be limited
implicit sight, which is apparently mediated by lower level centers
and remains completely unconsciousness. [AM]
The sense of self or
ego, which is related to the
ahamtattva is intimately
linked with the filters that limit the flow of
sensory perceptions into awareness. The filters tend to
limit inputs that are too divergent from the current world
view, while the filtering of perceptions reinforces the
current view. This holds for
both eastern and western psychologies. The attention
of the conscious mind is limited
and can focus on only one input at a time. In order to cover more
ground a part of the filtering system involves scanning over the
incoming signals for ones that match the filters, those that are
deemed to be of interest. All these systems are at some time
established with some amount of judgement, either conscious or
not, but in most cases once they are established they run on
automatic, becoming habitual.
The vast mass of incoming sensory waves do not pass
through the consciousness,
but are stored directly in the unconscious mind
, or the citta, without
being perceived. These include many innocuous
inputs that are omitted mainly to keep down the volume of
material sent to the conscious mind, but some are also omitted
precisely because they might upset the current sense of self
and the current conscious model of the world. All these waves
may, however, be recalled under
hypnosis, or resurface in
dreams or other ways. This vast bulk of unconscious memories serves
as the foundation of the waking
consciousness and will color it accordingly.
There are learning techniques in which the student listens to
music (with the conscious mind) and relaxes, while the information
to be learned is played at a lower volume and `heard' and remembered
directly by the subconscious mind. This may be related to various
subliminal techniques, where images are flashed for periods to short
to consciously register, or words are played to sleeping subjects.
It is noted that responses depend to some extent on content even
when the conscious mind is out of the loop.
Other perceptions or experiences may pass through the consciousness
but are too difficult to deal with and are "repressed",
and stuffed into the unconscious
parts of the mind. In western psychology these, repressed memories and
emotions are viewed as the main source for the formation of the
unconscious mind. In the eastern view repressed material is combined
with the larger flow of filtered sensory input discussed above. Repression
invests memories with energy and is actually another form of attachment. Alternately they may be
"projected" externally onto other people. [See also
below].
There is here the interesting issue of what makes it into
consciousness? Some of this is determined by biological priorities,
or the relation of information to ones ego or world view.
The interpretation of perceptions depends
on existing models, in which we often key on a few specific aspects of
something in order to give it meaning (e.g. the red aces of spades are
generally not seen). This involves the function of
memory. The earliest such model, which may serve as a reference point
for all others, is one's own body image.
[SFF]
See also the discussion of neuronal
memory and the coherent response of the brain to perceptions.
Physical perception in humans is geared to "useful" information,
which includes primarily changes in the environment. The brain is wired to be most aware of the
start and stop of a sensory signal. In the case of sight, the cones
of the eye are wired to emphasize edges etc. even before the signals
begin processing in the brain. There is therefore a level of selection
that occurs on the physical level, being inherent in the sensory organs
that limits what we can perceive of the world around us. Then from the
sense organ into the brain and through analysis there is a continual
process of simplification, reduction in information and integration
into larger wholes. This helps to maintain a relatively tractable
and stable model of the world and the self.[HB]
In processing the information that comes into the brain, the
comparison with memory and model,
provides a layer of meaning which is generally a part of what we
perceive. I.e. the red rectangle is a book, or an album cover, or a
piece of paper. The integration and interpretation necessary for
perceptions to have meaning is largely a function of the subconscious mind. It is with the
addition of "meaning" that the emotional
content of the perception is also added.
One main goal of this processing is stability, e.g. a cup is a
cup is a cup, even if rotated, or the lights are changed etc. Much
of the interpretation of sensory input aims to reduce the amount of
variation in the raw data, e.g. changes due to distance or light
levels. This leads in turn to a sense of predictability and control,
as well as highlighting the changes that we need to attend to. The
result is that the world we perceive
is much simpler and more stable that the actual world. Our world views
tend toward the simple and conservative side, in part due to
biological and mental needs to reduce the input to a manageable
minimum.[HB] The stability of our perception of colors given a wide
variation of incident light is an example of
this.
In an infant, initial definitions of objects are based on motion,
rather than appearance. I.e. if a partially obscured object (apparently
multiple objects) moves coherently it will be recognized as a single
object. Uniformity of color or texture is not generally sufficient. [SFF]
See Intuition.
Non-visual Perception
Consciousness and Perception
Stability of Perception
Development of Perception
Psychic Perception
