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Eva Wong and Noami Weisstein, 1983

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Sharp Targets Are Detected Better Against a Figure, and Blurred Targets Are Detected Better Against a Background. Eva Wong and Noami Weisstein, 1983. Overview. Background Figure vs. Ground Reversal Processing Differences Experiments Assumptions & Hypothesis Research Question

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slide1

Sharp Targets Are Detected Better Against a Figure, and Blurred Targets Are Detected Better Against a Background

Eva Wong and Noami Weisstein, 1983

overview
Overview
  • Background
    • Figure vs. Ground
    • Reversal
    • Processing Differences
  • Experiments
    • Assumptions & Hypothesis
    • Research Question
    • Design & Measures
  • Results
  • Discussion
background figure vs ground
BackgroundFigure vs. Ground
  • Rubin’s illusion
background figure ground reversals
BackgroundFigure-Ground Reversals
  • When “foreground” becomes “background” and/or vice versa
  • Widespread in art (according to Douglas Hofstadter, anyway)
background processing differences
BackgroundProcessing Differences
  • “Figure” aids detection of:
    • Contour discontinuity
    • Retinal image displacement
    • Line orientation
  • Possible Reasons:
    • Differential attention?
    • Differential resolution?
    • Differential sensitivity to spatial frequency?
the experiment assumptions hypothesis
The ExperimentAssumptions & Hypothesis
  • “Figure” and “Ground” represent different channels in the visual system
  • The channels have different functions:
    • “Figure” responsible for detail
    • “Ground” responsible for ‘global information’
  • Therefore:
    • “Figure” channel more sensitive to high spatial frequencies
    • “Ground” channel more sensitive to low spatial frequencies
the experiment research question
The ExperimentResearch Question
  • So, is the detection threshold:
    • lower in the figural regions for high spatial frequencies (such as a sharp target?)
    • lower in the ground region for low spatial frequencies (such as a blurred target?)

vs.

the experiment design measures
The ExperimentDesign & Measures
  • First Experiment
    • Purpose
      • Find observers who hold their (monocular) gaze regardless of what’s figure or ground
    • Procedure
      • Half of subjects initiate trial when the faces are figure; the other half initiate the trial only when the goblet is figure
      • The stimulus then appears in the blind spot at 50% probability
      • Measure detection accuracy; if different than chance, they’re not fixating!
the experiment design measures cont
The ExperimentDesign & Measures (cont.)
  • Second Experiment
    • Purpose
      • Establish luminance level where TP = 70% for both blurred and sharp targets
    • Procedure
      • Display sharp target at fixation cross at 50% probability
      • Change luminance until 70% accuracy is achieved for each of three blocks
      • Measure the final luminance value for each observer
      • Repeat for blurred target
the experiment design measures cont1
The ExperimentDesign & Measures (cont.)
  • Third Experiment:
    • Purpose
      • Determine accuracy of target detection against figure and against ground regions
    • Procedure
      • Target has a 50% probability of being presented
      • If target is presented (20 msec), it has
        • A 50% probability of being in the “goblet region”
        • A 50% probability of being in a “face region”
      • Measure TP and FP to estimate d’ and plot ROC
results
Results

Discrimination improves:

  • When sharp targets displayed in figure
  • When blurred targets displayed in ground

Off-fixation attenuates d’ by a “fixed magnitude”

  • Reflects an early processing constraint: retinal eccentricity
  • Caused by decreasing resolution with increasing distance from fovea
discussion
Discussion
  • Conclusions:
    • Different visual processes mediate the analysis of figure and ground
    • Accuracy not determined solely by attention, as defined by gaze or what is perceived as figure)
    • [Accuracy is also not determined solely by photoreceptor density]
    • “Global information extraction” may proceed faster than figure analysis
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