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

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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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