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

2. Outline 1)First steps and hypothesis generation – The Peter Jansen paradigm – Failures and revisions – The Vertical-Horizontal Illusion 2)Experimental Design 3)Results 4)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 Block 1 Block 2 Block 3 Reduction No feedback Valid feedback No feedback Control Strengthened Biased feedback No feedback

19. Method

21. 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 Phase 1 Phase 3 Difference Condition 1 Subject 1 -3.2651-2.661901.6032 Subject 2 -3.1660-2.50700.6590 Condition 2 Subject 3 -3.2703-4.0302-0.7593 Subject 4 -3.8623-4.4380-0.5757 Subject 5 -3.5175-3.51030.0072 Condition 3 Subject 6 -3.3370-4.0723-0.7353 Subject 7 -2.1695-1.81560.3539 Subject 8 -5.6957-3.80271.8930

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