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