Lecture Oct 23
Classic Issues In Perception
Speech perception is the last part- this is newer, not a "classic" issue in perception,
most of the topics we talk about will be "classic"
Today: space perception (perceiving depth, distance). Will typically be visual stuff,
but a little bit of auditory.
What we perceive tells us about the world- allows us to get around and live/
succeed/ not die. If we want to avoid a desk we can because of depth perception;
can avoid cars and see which ones are on the correct side, etc. All these things that
allow us to succeed in life are perceptions - perceptions give us accurate
information, how does this happen? How is it possible we can do this?
The input you're getting (what's arriving at your retina) is not 3D.. how do you make
it look 3D? What cues can you stick into it to make it 3D?
What are the cues that allow us to do this? What things are out in the world that
allow us to perceive depth? 3 types of cues:
1. Muscular (the muscle movements of the eye)
2. Monocular (looking at something with 1 eye)
3. Binocular (looking at something with 2 eyes)
The lens thickens and thins, as you look in the distance the muscle relaxes, lens gets
thinner. The thickness of your lens is a muscular cue, the process of accommodation.
This happens automatically.
Convergence: how together or apart the eyes must be, looking at something close,
your eyes go together (cross eye, kinda), look in the distance they diverge and go
These two things are cues our brain can be using to determine how much distance
between you and a thing.
These cues have some usefulness but it isn’t much and it's very limited, not so much
of a real cue.
Get from using one eye. These are the cues the painters had to use. 9 monocular
1. Interposition: (1)
2. Retinal image size: how big the thing is on your retina; things which are bigger
look closer. But relative sizes also come into play (small picture of a dog, with the
same retinal image size as a ball, we know the ball is closer because a ball is not
usually the same size as dog). Retinal image size accompanied by familiarity. Size
matters. (2) 3. Linear Perspective: As two parallel lines recede from you they look closer
together (3) Things that are parallel and more distant are closer together on your
4. Texture gradient: as you move in the distance, the texture changes; closer to you =
bigger and more dense, further from you = smaller and less dense
5. Height in the picture plane: When we have a picture there is a horizon. The
general perception is that things closer to the horizon look further away.
Used various angles, things closer to the horizon should have a higher exponent. If
you look, the power law works regardless of the angle, and the exponents work in
the way that as things move away in the sky (birds) our perception of distance
doesn’t grow as fast, but things on the horizon our perception of distance is more
sensitive. (in the sky our perception is growing slowly, don’t look as far away)
(check the textbook about this he makes no sense)
The moon illusion: the moon doesn’t not move