Group 4

Why is studying motion perception important?

SURVIVAL!!! For humans and other animals motion perception

is essential for maneuvering in everyday life.

Approaching motion represents a more immediate threat whereas receding motion represents opportunities. (Frost&Sun,2003)

Based on evolutionary thinking it would be expected that animals would be quicker to respond to immediate threats than to opportunities.

Previous research

Castet et al. (1993)Subjects viewed a moving oblique

line in comparison to a moving vertical line (standard)

Test subjects underestimated the speed of oblique lines compared to the vertical standard

The further away from vertical standard the more bias was evident

Previous research

Geesaman and Qian (1998)Subjects asked to compare speeds of

two different random dot patterns of same speed

Expanding random dot patterns were perceived as faster compared to the rotational and translational patterns

The speed of contraction pattern appeared slightly faster than the speed of expansion pattern.

Previous research

Sun and Frost (1998)

Examined neuron responses in pigeons when viewing a three-dimensional approaching object

Specific neurons fired only when the stimulus was approaching in a direct collision path with the bird’s head

Previous research

Lewis and McBeath (2004) Subjects observed a tunnel of tiles

that moved in either approaching or receding direction

Subjects were more likely to experience approaching motion

This effect decreased when stimuli pointed away from the subject

Previous research

Lewis and McBeath (2004) cont. Forward facing bias:

When the stimuli is oriented towards the subject the motion is more likely to be perceived as approaching

There are both adaptational and geometric reasons to favour the experience of approaching motion

Hypothesis

Approaching stimulus would be perceived as faster in comparison to a receding stimulus.

The stimulus would be perceived as

faster when presented at an angle closer to the collision path.

What experiment could be used to test this hypothesis???

Participants 5 subjects were recruited Range of age = 19-21 (Avg. 20) Normal to corrected vision 2 Experimenters were run and 3 naive

subjects

Apparatus Stimuli was displayed on 60 Hz Dell 17

inch monitor set at 1280 X 1024 pixels Used the application VirTools (with the

help of Dr. Sun) to create a 3D environment to display stimuli

Basic Task Have object move at 7 different speeds

at different angles Show the subject a “reference stimulus”▪ The stimulus moves at the middle speed

Show the subject a “test stimulus”▪ The stimulus moves at any one of the 7

speeds Ask subject to indicate which one was

faster

Initial Version of ExperimentBird’s eye view of the motion of the stimulus

Q: Was the second ball faster than the first ball?

Can anyone explain what is wrong with this experimental set up? The reference stimulus would always

move in the horizontal plane while the test stimulus moves at various angles

This would be like comparing apples and oranges

Second Version of Experiment

Bird’s eye view of the motion of the stimulus

Q: Was the second ball faster than the first ball?

Can anyone explain what is wrong with this experimental set up? What about the question? The path taken by the forward moving

stimulus is not the same as the path taken by backward moving stimulus

This would result in a difference in the size of the ball on the retina which could confound the results

New and Improved Version:

Bird’s eye view of the motion of the stimulus

Q: Which was faster? 1 or 2?

Psychometric Function

Results:

PSE – Point of Subjective Equality

Trajectory Path PSE approaching PSE receding

10/180 degrees

0.98 1.10

245/225 degrees

1.20 1.46

390/270 degrees

1.20 0.95

4.135/315 degree

0.94 1.32

Discussion

A general trend that approaching objects were perceived as faster compared to receding objects

However, a significant difference was only seen on the 135/315 trajectory.

Discussion

Geesaman and Qian (1998)With the expanding random dot

pattern, subjects would perceived the contracting pattern to be slightly faster.

The trend of lower PSEs for approaching test stimuli in our experiment contradicts this.

Discussion

The 90/270 trajectory (horizontal) showed no direction bias

Regan and Beverley (1973) They found that there are different

disparity detectors for horizontal and vertical motions

There was no directional bias in speed discrimination in the horizontal trajectory because they have a different disparity detector compared to the other three trajectories.

Discussion

Rind and Simmons (1999) There are neurons specifically

dedicated to avoidance reaction

Generalized to humans, this would explain the same essential system for what can be considered an avoidance reflex.

Discussion

At the 135/315 trajectories (path 4) the speed was perceived as faster to a greater extent than the same trajectory 45/225 to the right of the subject.

How would you interpret this possible leftward bias?

Discussion

How would you correct or improve the results?

Increase number of subjects Decrease the length of the experiment Increase the number of angles Three-dimensional goggles

Discussion

Give us specific activities where you would experience implications of this study? Driving training Better estimate collision time Sports – I.e. Baseball Videogames