Lightness and Brightness and Other Confusions

What Gregory is saying is that at the extreme edges of the retina the proximal
stimulus created no experience of anything, yet it triggered a reflex, an action
of rotating the eyes and head to bring the stimulus into the domain of seeing.
Gregory also points out that the prehistory of our vision is thus “embalmed in
our retinas”. (Ibid.) The cellular structures and processes being more primitive
the further they are from the fovea. He also reminds us “… it is eyes quite
high up in the evolutionary scale that produce signals in the absence of
movement”. (Ibid.) This would suggest that a proximal stimulus that triggers
an automatic reflex, but does not enter consciousness as an experience, does
not qualify for seeing.
Attention
Very often we have the experience of not seeing something that we know or
we are told is (or was) in our field of vision. Sometimes we fail to see things
happening before our eyes because our attention is focused on other things.
These distracting signals can be local parts of the global visual stimulus or
non-visual percepts, such as sounds or thoughts. ”Did you not notice that car
coming from the left?” asks the driving-instructor. ”No, I didn’t see it at all!”
replies the alarmed student, although the car (the distal stimulus) has caused,
without him knowing, millions of retinal and brain cells to fire in his head.
The student failed to pay attention to this particular visual percept, because
he was concentrating on other, perhaps even more pressing, stimuli or
thoughts. Our eyes and brains are being continually bombarded with potential
information about our surroundings and our relation to them. The act of
seeing is the effort to filter the relevant visual information from the irrelevant.
Looking is the act of attending to parts or levels of what is seen. Visual attention
has many levels and forms. If seeing is visual experience – and therefore
part of consciousness – we then require attention for seeing.
There is a very famous and quite entertaining demonstration, The Invisible
Gorilla by Christopher Chabris and Daniel Simons (1999), which illustrates
the selective power of attention. 41 On first viewing, many people do not notice
the gorilla amidst the basketball game. In fact they report that they did not
see it, and when the video is replayed to them many insist that it has been
changed (Chabris and Simons 1999). In other words, they had no experience
of the gorilla moving among the players, even though the stimulus must have
created all kinds of neural firing in their brains. One could also say that they
did not register the gorilla. The failure to see the gorilla resulted from the
observers concentrated attention to other features in the video. The message
of the demonstration is: this is happening to us all the time. We fail so see
large parts of the potential visual information reaching our brains.
41
See: www.theinvisiblegorilla.com/gorilla_experiment.html
40