The Effect of Object Size and Speed on Time to Collision Estimation in the Horizontal Plane Douna Montazer, Valdeep Saini, Nicole Simone, Danielle Thorpe
The Effect of Object Size and Speed on Time to Collision Estimation in the
Horizontal Plane
Douna Montazer,
Valdeep Saini,
Nicole Simone,
Danielle Thorpe
Initial Research Question
Does an object’s size have an affect on its perception of its speed…?
Time to Collision (TTC)
Time it takes for two objects to collide TTC Estimations: person’s judgment of time
to collision Previous research has been dedicated to
looming objects– Object size increases (or decreases) on the retina
Background Literature
DeLucia and Warren (1994)– Looming objects in subject’s central field of view– Results: larger objects had smaller TTC
estimations
Sidaway et al. (1996)– Study involved– Results: TTC estimates improved with increase in
the car’s velocity
Background Literature
Marini et al. (2000)– Studied whether the final size of the looming
object affected the accuracy of estimating TTC– Results: subjects rely on the size difference
between two stimuli when the objects were traveling at a faster speeds
However, at the slower speeds the subjects seemed to use a mental strategy to judge TTC (Tau)
Background Literature
Purpose of Current Experiment
Test the previous TTC findings within the horizontal plane (object’s size remains constant on the retina) – Examine the effects of size on TTC estimations– Examine the existing interaction between size and
speed during TTC estimations
Introduction
Conditions– 3 object sizes– 3 speeds– 3 disappearance points
Cognitive Bias?
Generally believed that larger objects tend to move slower compared to smaller objects– Could be due to a perceived increase in weight,
or perhaps the amount of effort one would need to move a larger object
Hypothesis
When presented at the same speed, larger objects will be perceived to move slower (have longer TTC estimations)
Subjects should have the best be best at TTC estimations for the smallest object at the highest speed
Questions
Design Ideas?
Method
Subjects– 15 subjects - 8 female and 7 male– Normal or corrected to normal vision– Subjects were naive to the experiment and our
hypothesis– Age range: 19-23 years old (M=21)
Method
Apparatus– Stimuli created in Microsoft paint and run through
Presentation software– Run on 4 computers
Method
Object speed (3 levels): 0.204, 0.324, and 0.421 pixels/msec
Object size (3 levels): 1 brick, 5 bricks, 9 bricks
Disappearing points (3 levels): 675, 500, or 325 pixels from barrier
Method
3x3x3 a total of 27 possible trial combinations
Both background and objects were of the same luminance
Method
Procedure– Subjects viewed computer screen at a distance of
75cm– The first block (27 trials) - practice and was not
included in data analysis
Method
A fixation cross appeared at the far right side of the screen
Object appeared and moved towards a stationary wall on the opposite side of the screen (left side)
At one of the disappearance points, both object and wall disappeared- screen turned black
Subject had to press spacebar when they thought the object would have hit the wall, had it not disappeared
After response, fixation cross reappeared on the right side of the screen and the next trial began
Demonstration
Method
Method
After every 10 trials, subject was given a 10 second rest period
There were 15 blocks within the experiment (each block containing 1 of each 27 trial combinations)
Data was analysed using Excel and SPSS
Results
When presented at the same speed, larger objects will be perceived to move slower (have longer TTC estimations)
Subjects should have the best TTC estimations for the smallest object at the highest speed
Results
3x3x3 within subjects ANOVA Main effect of Speed
– F(1.284, 28)=23.372, p<0.05
Results
Graph insert here Speed
Speed (pixels/ms)0.4210.3240.204
Dis
tan
ce F
rom
Ba
rrie
r (p
ixe
ls)
-60
-80
-100
-120
-140
-160
-180
-200
Main Effect For Speed
Results
3x3x3 within subjects ANOVA Main effect of Speed
– F(1.284, 28)=23.372, p<0.05
Main effect of Size– F(1.821, 28)=25.547, p<0.05
Results
Graph Insert here Size
SizeLargeMediumSmall
Dis
tan
ce
Fro
m B
arr
ier
(pix
els
)
-120
-125
-130
-135
-140
-145
-150
Main Effect For Size
Results
3x3x3 within subjects ANOVA Main effect of Speed
– F(1.284, 28)=23.372, p<0.05
Main effect of Size– F(1.821, 28)=25.547, p<0.05
Interaction of Speed and Size – F(3.027, 42.379)=3.221, p=0.032
Question
Improve on our Data Analysis– Additional Approaches
Discussion
Performance declined as both size of the object and speed increased
Overestimate distance and time regardless of speed and size
> accurate for small objects at slow speeds, < accurate for large objects at fast speeds
Discussion
Contradicts research– ↑speed ≠ ↑performance
↑ speed = greater differences between objects – Marini, et al.
Larger objects produced the least accurate TTC estimations at each of the three speeds
Discussion
WHY? Size
– Cognitive Bias– Changing number of bricks, not just size– Stresses importance of cognitive factors
Discussion
WHY? Speed
– Working Memory– Different Mental Strategies
Discussion
WHY? Speed x Size Interaction
– Combination of the previously mentioned explanations
Discussion
Limitations – Distance from observer to computer screen– SPSS data in pixels– Kept distance constant
Question
What are the implications of this research?
Discussion
Implications– Crossing the street– Police using radar guns
Question
What are some ideas for future research in this area?
How can you improve upon this research?
Discussion
Future Research– Real-life situations– practical/familiar objects– Effect of expertise