Chapter 4

Question 1

Explain why detecting edges is fundamentally important for object recognition.

Answer 1

we need edges to be able to see objects, its how we distinguish them

Question 2

Describe the “Pandemonium Model” of object recognition

Answer 2

~ feature demons are connected to cognitive demons (like pattern recognizers) and then decision demons. Biologically implausible, doesn’t work.
~ model of letter recognition, nothing in nervous system that acts as decision demon (no neuron or signal)

Question 3

Describe figure/ground perception. What are bistable images?

Answer 3

figure: sharply defined shape/object
ground: the remainder (background)
Bistable images: can be perceived 1 of 2 ways (i.e. necker cube); switches back and forth between two perceptions from fatigue

Question 4

Describe the “Gestalt” school of Psychology.

Answer 4

(Designed against structuralism) focuses on why objects are grouped together perceptually. It stresses the top down processing. The perceptual whole is greater than the sum of its parts.

Question 5

What are the Gestalt grouping principles?

Answer 5

texture
occlusion
proximity
connectedness
common fate
closure
good continuation
symmetry
similarity

Question 6

What is the Law of Pragnanz? Why is it important? What happens when we “trick” the brain into applying it inappropriately?

Answer 6

~The law of Pragnanz is when we automatically perceive the simplest, most stable figure of all possible alternatives.
~We construct what should be there rather than what is there. We can trick the brain into seeing things that aren’t there (Kaniza figures).
~These geometric shapes are not there but the brain constructs their presence because it’s very unlikely that they are not there. Illusions (illusory contours)

Question 7

Define priming and how it can affect object perception.

Answer 7

~ exposure to stimulus at time 1 affects exposure to stimulus at time 2.
~ can make you faster and more accurate for time 2.

Question 8

How does the visual system deal with occlusion?

Answer 8

1. relatability: the degree to which two line segments appear to be part of the same contour
2. nonaccidental features: a feature of an object that is not dependent on the exact (or accidental) viewing position of the observer. Arrow junction, y-junction & t-junction.

Question 9

Describe the global superiority effect

Answer 9

~we see global aspects more quickly. Low spatial frequencies are processed before high spatial frequencies.
~HCL example in class (saw HCl before the SNU, process global before local objects)

Question 10

Discuss the template theory of object recognition. What is the major problem with this theory?

Answer 10

~ have neuron with receptive field that matches object.

~ not biologically plausible, there are too many objects (example-different fonts for letters)

Question 11

Discuss the “recognition by components” theory of object recognition.

Answer 11

~Biederman-all objects can be made up of simpler, 3-D forms called geons (geometrical icons). Simple, efficient theory

Question 12

Discuss the “feature integration model” of object recognition.

Answer 12

1. preattentive stage: immediately extracts & processes sensory info (primitives)
   primitive texture features= textons (major differences In texture pops out)
2. focused attention stage: requires conscious effort
   (e.g. serial search: examine each element)

Question 13

Describe the computational approach to object recognition.

Answer 13

1. primal sketch: edges
2. 2 1/2-D sketch: viewpoint dependent
3. 3-D model representation: how objects relate to each other

Question 14

Why does the perception of faces seem to be special?

Answer 14

We have a specific area in the brain devoted to detecting faces. Provides a great deal of information (Gender, emotion, age, health/reproductive fitness, identifying specific individuals)

Question 15

Discuss the area of the brain involved with facial perception and recognition. What happens if this area is destroyed?

Answer 15

~ Fusiform Face Area (FFA): perception of upright faces
right inferior temporal lobe
~ damaged: prosopagnosia (inability to recognize faces). can be acquired or developmental

Question 16

Discuss evidence that the brain area involved with facial recognition may be more generally involved with expert object recognition.

Answer 16

Gautier & Tarr’s Greeble Study
trained people to become experts at (new groups of objects) greebles
monitored FFA
more activity as more skilled
we can train FFA so we can recognize other classes of objects