Sharp Targets Are Detected Better Against a Figure, and Blurred Targets Are Detected Better Against ...
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Eva Wong and Noami Weisstein, 1983 PowerPoint PPT Presentation


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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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Eva Wong and Noami Weisstein, 1983

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Eva wong and noami weisstein 1983

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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