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Perception of wholes and of their component parts: Some configural superiority effects. Pomerantz , J. R., Sager, L. C., and Stoever , R. J. (1977). Journal of Experimental Psychology: Human Perception and Performance , 3 , 422-435. Introduction.

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perception of wholes and of their component parts some configural superiority effects

Perception of wholes and of their component parts: Some configural superiority effects

Pomerantz, J. R., Sager, L. C., and Stoever, R. J. (1977). Journal of Experimental Psychology: Human Perception and Performance, 3, 422-435.

introduction
Introduction
  • Feature detectors have sometimes been presumed to operate independently of one another.
  • But the independent assumption has difficulty in explaining certain context effects in perception, e.g. Gestalt phenomenon.
  • In Gestalt, there were 2 claims
    • The appearance of one element in the visual field was influenced heavily by elements nearby
    • The perception in general could not be characterized as the simple sum of independent features or sensations
introduction context aiding perception
Introduction – context aiding perception
  • Two sides of stories
    • Interference: context acts to impair perception
      • Context may adds noise to the perceptual system, overloading or otherwise disrupting its normal operation.
      • Explanation of word superiority effect:
        • Perceptual interpretation
        • Postperceptual interpretation (preferred)
    • Aiding: context could aid perception itself
      • Context could aid perception itself, rather than some postperceptual process.
      • Context influenced perception, but always in a harmful way. (Homa, Haver, & Schwartz, 1976)
      • Schendel and Shaw (1976) found a beneficial effect of context, which parallel the result in word superiority effects.
      • Context improving discrimination, even though it does not show that the effect is necessarily perceptual in origin.
purpose
Purpose
  • To explore in more detail the possibility that context can improve perception itself.
  • That is, clarifying the conditions under which context might aid perception and with localizing the stage of processing at which context would have its effects
experiment 1
Experiment 1
  • Pomerantz and Garner (1973) showed that subjects perceived two curvature elements as a whole.
  • Failure of selective attention was therefore proposed as an operational measure of perceptual grouping.
  • Pomerantz and Schwaitzberg (1975) found that two-choice RTs increased when the elements were moved further.
  • In this experiment, they tested whether having a constant element nearby actually improved performance.
experiment 1 method
Experiment 1 – method
  • Context condition: ( ) ‧ ) )
  • No-context condition: (‧)
  • Two-alternative RT task
  • 8subjects
  • 3 blocks, order of conditions within blocks was counterbalanced across subjects
  • Each condition consisted of 72 stimulus, divided equally between two stimulus.

()

()

))

Is the target “(“ or “)”?

Auditory

warning signal

200 ms

experiment 1 result
Experiment 1 – result
  • Mean correct RT for the context condition was 421 ms.
  • Mean correct RT for the no-context condition was 444 ms.
  • The difference is significant. (p < .05)
  • Configural superiority effect was obtained even knew both the location and the identity of the stimulus alternatives beforehand.
experiment 1 discussion
Experiment 1 – discussion
  • Stimulus must be held in memory and recognized, and then selected and executed the proper response.
  • Next step is to clarify whether the effect is a perceptual one?
    • Recognize faster?
    • Easier to associate with the required response?
  • What is the contexts that impair perception instead of facilitating it?
    • If all contexts help, …
      • It could be explained by lateral enhancement and the claim that context converts an absolute judgment into a relative one.
      • Any context providing a similar positional anchor should be helpful.
    • Otherwise, …
      • It can’t be explained by lateral enhancement.
experiment 2
Experiment 2
  • Perceptual alone?
    • Employed task with minimal memory demands
    • To indicate the location in the field of the odd stimuli, and neither the set of possible stimuli nor an arbitrary response code need be remembered.
    • If effect remains, it can be assured that the effect is perceptual in origin.
  • All context?
    • The possible important factors of previous stimuli are:
      • Mirror image
      • Bilaterally symmetrical
    • Experiment 2 use different stimulus to control the two factors.
experiment 2 method
Experiment 2 – method
  • 12 subjects were used.
  • Decide which quadrant contained the disparate elements.
  • Each array was presented 4 times, with the first time always be treated as practice and not scored.
experiment 2 result
Experiment 2 – result
  • Replicate the result from experiment 1
experiment 2 result1
Experiment 2 – result
  • Destroy the original grouping structure.
  • No superiority effects.
  • It is unlikely that the effect found in A, B and C was due to lateral enhancement.
experiment 2 result2
Experiment 2 – result
  • Basic superiority effect did not depend on regular spacing of the stimuli.
  • Mirror image and bilateral symmetry were not the factors that improve the emergent of context.
experiment 21
Experiment 2
  • Unusually long reaction times were obtained in experiment 2.
    • Simply difficult to see?
    • Performance may be process limited rather than state limited.
  • Can the effect be obtained with other types of simple perceptual discrimination?
experiment 3
Experiment 3
  • Different discrimination:
    • Orientation of a curved line segment
    • Position of a line relative to a fixed point
    • Positive v.s. negative diagonal line
    • Horizontal v.s. vertical line
    • Line length
  • Larger size to eliminate limitation in processing.
experiment 3 result
Experiment 3 – result

Baseline condition

  • Context per se does not automatically help or hinder perception.
  • Certain contexts help, while others hinders.
experiment 4
Experiment 4
  • Word superiority effects may vanish when the subject can prepare himself for the kind of discrimination he will have to make.
  • Whether the same would be true for the this superiority effect?
experiment 4 method
Experiment 4 – method
  • The method and procedure are similar to experiment 2 and 3.
  • Block designed with counterbalanced order
  • 2 blocks with 32 stimulus exposure each  practice trials
  • 3 more replications of the 2 blocks were counted
experiment 4 result
Experiment 4 – result

RT : 1,480 ms 641 ms

  • Configural superiority can emerge even when the subject has foreknowledge of the exact discrimination he will have to make on each trial.
  • The long RTs were reduced.
experiment 4 discussion
Experiment 4 – discussion
  • We can obtain the effect with a number of elementary perceptual discriminations and in both classification and oddity tasks.
  • Seemed to be free from memory involvement.
  • It is not obvious what component processes are involved in performing an oddity task
    • array may be processed serially or in parallel model.
experiment 4 discussion1
Experiment 4 – discussion
  • To test the processing model of superiority effect, the set size should be alternated.
  • In serial model, …
    • The time required to locate the odd stimulus should grow with the size of the array to be processed.
  • In parallel model, …

 The disparate stimulus spontaneously segregates regardless of the number of background stimuli.

experiment 5
Experiment 5
  • Measured the time required to determine whether any stimulus in an array is different from the others, as a function of the number of the stimuli in the array.
  • Detection task with stimulus same as experiment 4, and press when detect a disparity
  • 3 conditions:
    • No context(NC)
    • Good context (GC)
    • Poor context (PC)
  • 3 set sezes:
    • 2, 4, and 6
  • All intermixed
  • All position has equal chance
  • 50% absent, 50% detection
experiment 51
Experiment 5
  • GC has fastest RT, while PC show the lowest.
  • Display size had virtually no effect with the GC arrays, while had large effect on the PC arrays.
  • Within NC arrays, for all subjects, the RTs were longest when the arrays contained just four stimuli.
experiment 52
Experiment 5
  • When an array contains just diagonal lines with no context, the lines appear to interact to form larger configurations.
experiment 5 discussion
Experiment 5 – discussion
  • GC arrays: parallel feature-inhibition model
  • PC arrays: serial-memory model
  • Subjects processed the no-context arrays as holistic configurations, which is itself another instance of configural dominance.
conclusion
Conclusion
  • Context can improve discriminability.
  • Context appears to have its effect directly on perceptual components of discrimination.
  • How does context improve discriminability?
    • Context changes an absolute judgment into a relative one by providing an anchor
    • Context interacts with the target to form emergent features
conclusion1
Conclusion
  • Novel features happen to be more discriminable than the features contained by the targets without context.
  • Emergent features could be detected indirectly by integrating the output of detectors for simple parts.
  • Emergent features serve as functional units in perception, regardless of whether they are detected directly or are derived from simple parts.
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