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 Design3) Results4) 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
DesignBlock 1Block 1 Block 2Block 2 Block 3Block 3
ReductionReduction No No feedbackfeedback
Valid Valid feedbackfeedback
No No feedbackfeedback
ControlControl No No feedbackfeedback
No No feedbackfeedback
No No feedbackfeedback
StrengthenStrengtheneded
No No feedbackfeedback
Biased Biased feedbackfeedback
No No feedbackfeedback
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
+
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ResultPhase 1Phase 1 Phase 3Phase 3 DifferenceDifference
Condition 1Condition 1
Subject 1Subject 1 -3.2651-3.2651 -2.66190-2.66190 1.60321.6032
Subject 2Subject 2 -3.1660-3.1660 -2.5070-2.5070 0.65900.6590
Condition 2Condition 2
Subject 3Subject 3 -3.2703-3.2703 -4.0302-4.0302 -0.7593-0.7593
Subject 4Subject 4 -3.8623-3.8623 -4.4380-4.4380 -0.5757-0.5757
Subject 5Subject 5 -3.5175-3.5175 -3.5103-3.5103 0.00720.0072
Condition 3Condition 3
Subject 6Subject 6 -3.3370-3.3370 -4.0723-4.0723 -0.7353-0.7353
Subject 7Subject 7 -2.1695-2.1695 -1.8156-1.8156 0.35390.3539
Subject 8Subject 8 -5.6957-5.6957 -3.8027-3.8027 1.89301.8930
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