Longer or Shorter?

1. Longer or Shorter? An examination of line length discrimination using manipulated feedback Amanda Hostiuc, Alicia Kim, Melanie Laking, and Matt Pachai

2. Outline • First steps and hypothesis generation • The Peter Jansen paradigm • Failures and revisions • The Vertical-Horizontal Illusion • Experimental Design • Results • Conclusions

3. The Peter Jansen Paradigm • The original task flashed two lines on screen simultaneously and asked if the second line was longer or shorter • This experiment served as the starting point in our research program

4. The Original Motivation • What is the effect of attention on our line length acuity in the Peter Jansen paradigm? • Could attentional cueing lead to increased performance on a length discrimination task? • Would an invalid cue decrease performance?

5. A Snag in the Literature • A disturbing picture began to emerge • Many articles described the “well known fact” that vertical lines are perceived as longer than horizontal lines

6. The Vertical-Horizontal Illusion • When a horizontal line and a vertical line of the same length are presented together, the vertical line is perceived as on average 10% longer

7. Craven (1993) • Systematically examining the perception of

8. The New Design • We decided it was unlikely that cuing would cause a significant change in like acuity if our perceptions are already biased • But what if we could change the perception of the illusion? • How might you go about designing an experiment to manipulate

9. Programming a Pilot Run • We decided to program our experiment from scratch in Matlab due to prior experience • After extensive tweaking, Amanda and Melanie ran as control subjects • The result • NO vertical-horizontal illusion was present!

10. Back to the Drawing Board • After our initial failure, we began to scour journal articles to find an ex

11. Vertical-Horizontal Illusion • Vertical-Horizontal Illusion (V-H) • Perception of vertical lines as longer than horizontal

12. Purpose • Increase or eliminate vertical-horizontal illusion

13. Idea Generation (edit) • Consecutive lines • Cues • Same/different • Shorter/longer • Feedback • Correct • biased

14. Herzog and Fahle, 1999 --Vernier Task

15. Hypothesis • Valid feedback • Decrease V-H • Biased feedback • Increase V-H

16. Method • Conditions • Reduction: valid feedback • Control: no feedback • Strengthened: biased feedback

17. Method • Blocks (Phases) • Block 1: establish baseline threshold • Block 2: learning trials • Block 3: examine the effect of learning trials compared to baseline threshold

18. Design

19. Method

20. Method

21. Method • Subjects • 8 subjects • Stimuli • Vertical/horizontal lines between -9 to +3 pixels

22. Method • Measure • Accuracy of the responses • Trials • 10 practice trials • 240 trials for each block • 20 trials per length per block • Total of 720 trials

23. Method • Procedure • Fixation cross • Mask • Stimulus • Response: left or right

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30. Result

31. Results (Condition 1)

32. Results (Condition2)

33. Results (Condition 3)

34. Results • Replicated the v-h illusion • Inconclusive results in reducing/ strengthening the illusion with valid/biased feedback

35. Discussion • Finding 1: Vertical-horizontal illusion was replicated • Craven (1993)

36. Discussion Finding 2: • Unable to decrease illusion using valid feedback Finding 3: • Unable to increase illusion using biased feedback

37. Discussion Source of error • Number of trials • Number of N

38. Discussion Suggestions for future research • More time to train/learn • More trials for Block 2 • Better incentive