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Vertical Horizontal Illusion

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Vertical Horizontal Illusion Powered By Docstoc
					              Longer or Shorter?

An examination of line length discrimination using
             manipulated feedback


     Amanda Hostiuc, Alicia Kim, Melanie Laking, and Matt Pachai
                     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
     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
       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?
         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
   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
              Craven (1993)
• Systematically examining the perception of
             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
       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!
      Back to the Drawing Board
• After our initial failure, we began to scour
  journal articles to find an ex
      Vertical-Horizontal Illusion
• Vertical-Horizontal Illusion (V-H)
  – Perception of vertical lines as longer than
    horizontal
                   Purpose
• Increase or eliminate vertical-horizontal
  illusion
         Idea Generation (edit)
• Consecutive lines
• Cues
  – Same/different
  – Shorter/longer
• Feedback
  – Correct
  – biased
Herzog and Fahle, 1999 --Vernier Task
                   Hypothesis
• Valid feedback
  – Decrease V-H
• Biased feedback
  – Increase V-H
                   Method
• Conditions
  – Reduction: valid feedback
  – Control: no feedback
  – Strengthened: biased feedback
                     Method
• Blocks (Phases)
  – Block 1: establish baseline threshold
  – Block 2: learning trials
  – Block 3: examine the effect of learning trials
    compared to baseline threshold
                   Design
               Block 1    Block 2    Block 3


 Reduction        No        Valid       No
               feedback   feedback   feedback
  Control         No         No         No
               feedback   feedback   feedback
Strengthened      No       Biased       No
               feedback   feedback   feedback
Method
Method
                    Method
• Subjects
  – 8 subjects
• Stimuli
  – Vertical/horizontal lines between -9 to +3 pixels
                      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
                     Method
• Procedure
  – Fixation cross
  – Mask
  – Stimulus
  – Response: left or right
+
+
                          Result
                          Phase 1   Phase 3    Difference
Condition 1
              Subject 1   -3.2651   -2.66190    1.6032
              Subject 2   -3.1660    -2.5070    0.6590
Condition 2
              Subject 3   -3.2703   -4.0302     -0.7593
              Subject 4   -3.8623   -4.4380     -0.5757
              Subject 5   -3.5175   -3.5103     0.0072
Condition 3
              Subject 6   -3.3370   -4.0723     -0.7353
              Subject 7   -2.1695   -1.8156     0.3539
              Subject 8   -5.6957   -3.8027     1.8930
Results (Condition 1)
Results (Condition2)
Results (Condition 3)
                   Results
• Replicated the v-h illusion
• Inconclusive results in reducing/
  strengthening the illusion with valid/biased
  feedback
                    Discussion
• Finding 1: Vertical-horizontal illusion was
  replicated
  – Craven (1993)
                 Discussion
Finding 2:
• Unable to decrease illusion using valid
  feedback

Finding 3:
• Unable to increase illusion using biased
  feedback
                  Discussion
Source of error
  – Number of trials
  – Number of N
                  Discussion
Suggestions for future research
  – More time to train/learn
  – More trials for Block 2
  – Better incentive

				
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