15. object recognition

Question 1

2 approaches for object recognition?

Answer 1

1. recognition by components
2. viewpoint-specific

Question 2

Recognition by components?

Answer 2

• use geons to assemble and recognize a whole object
• A model of object recognition that proposes that recognizing an object depends on first identifying the object’s basic 3-D shapes and how they fit together.

Question 3

Evidence for recog. by componenets?

Answer 3

• we can rec. an object even if we only have some of its geons
• its really difficult to identify an object if you can’t identify geons

Question 4

Limitations of recog. by components?

Answer 4

• it achieves invariance… but its often too abstract
• ALL briefcases would look the same, couldn’t DISTINGUISH between them
• the model is too extreme

Question 5

viewpoint-specific meaning?

Answer 5

• objects are recognized based on view-specific representations stored in memory
• ie. multiple representations, for each possible view, are stored at the same time

Question 6

Evidence for viewpoint-specific?

Answer 6

• artificial objects are recognized more quickly when seen from a familiar viewpoint

Question 7

Limitations for viewpoint-specific?

Answer 7

• do we have enough room in our brains to store all the different representations we would need?? (no)

Question 8

Grandmother cell?

Answer 8

• truly invariant –> responds to an image of a toaster and the concept (word) toaster
• can’t be used to guide action
• debated, cuz it would require enormous amounts of neurons for all objects and concepts
• A neuron that responds to a particular object at a conceptual level, firing in response to the object itself, a photo of it, its printed name, and so on.

Question 9

Top-down meaning? What kind of information?

Answer 9

cognitive influence on perception

• perceiver’s goals
• attention
• prior knowledge
• expectations ab what objects are likely to occur in the current scene

Question 10

Bottom-up meaning?

Answer 10

based only on stimulus

Question 11

How does the “gist” affect object recognition? Vice versa?

Answer 11

• We’re much worse at identifying objects when they’re at an atypical location in the scene or in an inappropriate scene
• We’re much better at identifying the correct scene (background) if the object and scene are correct

Question 12

How are recognition of the gist and the object related? —> When?? What helps what?

Answer 12

• we likely process both at the same time
• after identifying “gist” –> top down expectations of what objects are most likely to be in certain scenes help with object recognition

Question 13

Bayesian approach?

Answer 13

• visual system uses 2 probabilities to infer the scene from the retinal image:
  1. prior probability of all scenes
  2. for each scene, probability that it produced the current retinal image
• use of mathematical probabilities to describe the process of perceptual inference

Question 14

Spatial frequency def? What does high vs low look like?

Answer 14

• describes periodic distribution of light and dark in an image
• low: fuzzy, big blobs of color
• high: only fine details, little/no color

Question 15

Units for spatial frequency?

Answer 15

• Cycles per degree
• more cycles = higher sp. frq.

Question 16

Degrees of visual angle?

Answer 16

• angle measure (in degrees)between the rays on either side of an object
• specifies the size of an object on the retina
  –> 1 to 1 correspondence

Question 17

Spatial frequency channels? Perception of sp. frq?

Answer 17

• neural mechanisms that are sensitive to only a narrow range of spatial frequencies
• neurons / general perception is NOT equally sensitive to all spatial frequencies!

Question 18

Contrast sensitivity function shows? (axis?)

Answer 18

Axes:
x: relative sensitivity
y: sp. frq. (cycles per degree)

• we are most sensitive to INTERMEDIATE spatial frequencies

Question 19

How does moving closer/further affect sp. frq?

Answer 19

Closer –> REDUCES sp. frq
–> closer usually helps

Further –> INCREASES it

Question 20

You’re looking at something with high sp. frq. To make it easier to see, should you move closer or farther?

Answer 20

CLOSER

Question 21

You’re looking at something with low sp. frq. To make it easier to see, should you move closer or farther?

Answer 21

FARTHER

Question 22

You’re looking at an object. When you move closer to it, it becomes harder to see. Does the object have high or low sp. frq.?

Answer 22

LOW