Describe how reaching and grasping abilities develop in the first year of life.

Lecture 7: Development of reaching

Within first 2 weeks, babies already directing arm towards objects. Some crude control of reach direction.

Improves by the 5th month; consistently touch targets.Won’t reach for targets beyond arm’s length.

Catching and anticipating target motion at 6 months.

Distance accuracy develops more slowly, improving by 7 months.

Sketch the response of the photoreceptors. How do rods and comes differ? How does the response change with light intensity?

Photoreceptor response to light

Rods are more sluggish than cones

Brighter lights lead to a faster response

40msec

150msec

Response lasts 300msec to over 1 sec

Response lasts 50- 150 msec

Useful website for understanding statistics

http://onlinestatbook.com/rvls/index.html

Suppose you have a random variable, such as height of the UT student population. This population has a standard deviation of S. Take a sample of size N from the population, and calculate the sample mean, M. Do this many times. What is the standard deviation of M?

SEM = S/√N

What is visual search? What factors influence search?

Lecture 12 – slides 4-18

Process by which a region of the peripheral retina is selected as the targetfor a saccade (“overt attention”) or simply attended ( “covert attention”)

Factors: simple versus complex stimulus properties, number of items, context,Spatial memory

How does visual memory affect perception? Give examples.

Affects where you look in a scene.

Speeds visual search.

May facilitate change detection.

Subjects should be more sensitive to changes in familiar environments than to unfamiliar ones because the memory representation is well-defined.

Kit et al: 3 days in a virtual apartment searching for objects.On day 3, the color of 3 objects was changed.Question: does the color change attract gaze?

Increased probability of looking at changed objects.

Uke-Karacan & Hayhoe.

If subjects become familiar with an environment, are changes more likely to attract attention?

General Design: Subjects walked along a footpath in a virtual environment including both stable & changing objects while avoiding pedestrians.

Procedure

• Two groups:– Inexperienced Group No familiarization trials– Experienced Group 19 familiarization laps before the

changes occurred

Results

• Total gaze duration on changed objects were much longer after experience in the environment.

• Fixation durations on stable objects were almost the same for the two groups.

Stable Objects Changing Objects

Experienced

Inexperienced

Average gaze duration/object/lap

Effects of Different Changes

Stable Replaced

Disappeared Moved New

Experienced

Inexperienced

Change Blindness

• Probability of being aware of the changes was correlated with gaze duration on the changing objects (rho=0.59).

• Awareness of the changes was low, suggesting that fixations are a

more sensitive indicator. • Change blindness in the natural world may be fairly uncommon, because most scenes are familiar.