Size constancy and brightness constancy are the only constancies we're talking
Howing (Halway?) and Boring experiment: the intersection of the two hallways,
make the circle at the end of the hallway smaller or larger- setting the size of the
object. Other hallway is longer, and the experimenter made the circle always at 1
degree of visual angle (make it smaller when you get closer, when it gets further
make it bigger- to keep it the same size on your retina), correlation between the size
of the object and the distance of it. (1)
People must be able to accurately perceive distance, that’s how they can maintain
size constancy. If we take away distance cues, their size constancy should go away
(don’t know how far away it is, can't judge how big it is). Removed all cues (dim
lights, or turn them off, remove pictures or things from walls, remove the binocular
cue or retinal disparity and make them look through a tube with one eye), this
destroyed size constancy- when you're asked to rate how big the thing is, you
always see it as the same size (1 degree of visual angle on your retina no matter
where it is, can’t maintain size constancy, so it always looks the same size no matter
where it is) (2).
The key to perceiving size accurately is to perceive distance, then you take the two
things into account.
The moon illusion: things overhead are perceived as being closer and therefore
smaller. The moon is always the same distance away. When the moon is on the
horizon it looks bigger because things near the horizon are perceived as being
bigger away. Overhead it looks closer than it looks on the horizon, but it's the same
size, so we assume that that moon must be smaller because it is closer. (3)
When you contrast lines that have arrowheads, the line with the inward arrow
heads (a) looks shorter than line b. Why? Line a seems to be closer to you than line b
(see c) so they don’t look the same size. Same thing on your retina but one (a) looks
closer, so you assume it must be smaller
Look up the Ponzo Illusion
Brightness constancy: something is as bright as it is, whether the lighting is limited
or strong you see the thing as the same brightness. The ability to know the
brightness of the thing aside from the ambient lighting in the environment. How do
you do that?
In an airplane, look down and everything looks like little toys, you don’t have the
ability to equate this. First time in an airplane you look down and think its toys
because you've blown your ability to perceive the size accurately- you don’t have
experience with it because you've never done it before, you can get used to this. Back to brightness constancy…
(4) Katz (sp?) (1911?) created a box, equate the brightness (add more black =
darker gray, etc).
Second part: put a bright lamp that shines on the experimenter's ball, the subject
can see the lamp. (5) If the subject can maintain brightness constancy the lamp
shouldn’t make a difference and should be able to equate the balls and not be fooled.
(6) put up a board with eyeholes so people can only see the spinning balls, they
cannot see the lamp so they cannot take this into account, the brightness constancy
is blown - they cant take into account information they don’t know about. When you
know the conditions, you can account for them.
However, Katz is wrong.
Gell (1921); can create a situation where the ambient lighting can be taken into
account and people still couldn’t get brightness consistency right. (7) see a grey
circle when a light is shone on the black wall. Show people what's going on- take a
white piece of paper on a string from above and slowly lowered it into the beam of
the spotlight, people can tell that it's a light, and that it's actually a black wall -
people suddenly know the reality of the situation. People can perceive accurately
now because they can take things into account. Remove the paper, what happens?
Go back to viewing black wall with a grey disk; this perception starts up again. You
again think the wall is grey on the spot the light is shining. You know all the
information you have to take into account but you don’t do it- knowing the reality is