Perception
Psych 293
Spring 2015
Exam 3 Answers
There were 150 points. Each question was worth 15 points.
1. Reflectance is the ratio of amount of reflected light divided by the amount of incident light. It is a physical quantity. The corresponding psychological experience is what Gilchrist called lightness, a word the he uses often in your reading of him from his website and from his assigned article. Lightness constancy is the evidence that we perceive something like reflectance. The problem is that the light to the eye from surfaces that have lightness is all reflected light. We are very poor at sensing the amounts of incident light. The problem, then is: How do we perceive lightness from only reflected light? Some of you confused reflected light with reflectance.
2. An anchoring rule is needed to specify where, on the gray scale, a particular neutral color is. Wallach asserted that when the ratio of amounts of light in two areas was the same, then the grays would be the same grays. Gilchrist pointed out that this did not say how light or dark the grays would be. To say where a gray is on the scale requires an anchoring rule. Gilchrist showed people a display with only two grays in it by coloring a dome with two grays and having people look inside the dome so that they could see nothing else. In these displays, even if two grays were both fairly dark, people saw the lighter gray as white and the other as a little darker, but also light. There was no black seen in these displays. Gilchrist argued that this was evidence for the greatest luminance anchoring principle.
3. The significance of this stereo pair is that there is no recognizable pattern in either image, but that disparity can be defined in the relation between them, and stereopsis can result from that disparity. This undercut the Gestalt psychology idea that the images in the two eyes are matched up by recognizable patterns.
4. Your labeled diagram should show the receptors (rods and cones), bipolar cells, and ganglion cells arranged in sequence. The horizontal connections across the rods and cones are achieved by the horizontal cells and the horizontal connections at the ganglion level are achieved by amacrine cells.
5. The diagram is a caricature of retinal receptors (on top) and ganglion cells on bottom. The numbers across the top represent amounts of light that are supposed to affect the receptors proportionally. According to the conventions we adopted in class, the number at the top is carried through positively to the ganglion cell immediately below. The amount of inhibition coming from connections to a receptor is equal to the facilitation but divided in half, so half of the value of the number at the top goes to each side as inhibition. Each ganglion cell has both facilitation and inhibition acting on it. When you add these up, the middle ganglion cell will have a value of -10; the two beside it will have values of +5; and all the others will have the value of 0.
6. The “Hallie Berry” cells are different because they give the same response to anything that the person recognizes as referring to Hallie Berry (or Jennifer Aniston or the Sydney Opera House). For Hallie Berry, her masked appearance as “Catwoman” and her written name gave the same response. The receptive fields that we looked at before all had some shape characteristic — a point, a line, a moving line, or a monkey paw shape. The “Hallie Berry” cells clearly were not responding directly to a shape on the retina.
7. The three records refer to one display and one set of colors, so even though you need to use the information from all 3, you need label only one. An area that is white in all 3 is white; dark in all 3 is black, light in only the long wavelength record is red, light in only the middle wavelength record is green, and light in only the short wavelength record is blue.
8. Black per se cannot be projected onto a screen. Only light can be projected from a projector. That is why it is misleading to say that black is projected. Black is the result of contrast between a lighted area and a less lighted area. If there is a great deal of light surrounding an area, the surrounded area will look black.
9. If you had a cell whose receptive field had a center-surround structure, it would either be a ganglion cell or an LGN cell according to what we’ve studied so far. If the light were increased to cover both the center and the surround at the same time, lateral inhibition would operate to cancel out the two effects so that the net result would be zero. It would be the same as if no light were shining on the receptive field.
10. Gestalt laws that you could cite and illustrate are the “Laws” of proximity, good continuation, similarity, symmetry, and closure for example. The Gestalt psychologists (there was no person named Gestalt) recognized that many aspects of our experience are so obvious that we take them for granted and don’t think that they need explaining. They devoted much effort to make people realize just how much of their everyday experience ivolved organized patterns and that it was important to make researchers realized that the organization in experience needed to be explained.