Group 4

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.

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

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.

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

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

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

 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 = (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

Methodology  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

Methodology  Initial Version of Experiment Bird’s eye view of the motion of the stimulus Q: Was the second ball faster than the first ball?

Methodology  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?

 PSE – Point of Subjective Equality Trajectory PathPSE approachingPSE receding 1 0/180 degrees /225 degrees /270 degrees /315 degree

 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.

 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.

 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.

 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.

 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?

 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

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