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Experimental Psychology PSY 433

Experimental Psychology PSY 433. Chapter 7 Perception (Cont.). DVs in Perception Experiments. Verbal descriptions of experience. Imprecise. Not immediately verifiable. Reaction times. Reports that can be verified: What did you see?

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Experimental Psychology PSY 433

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  1. Experimental PsychologyPSY 433 Chapter 7 Perception (Cont.)

  2. DVs in Perception Experiments • Verbal descriptions of experience. • Imprecise. • Not immediately verifiable. • Reaction times. • Reports that can be verified: • What did you see? • Confidence ratings – how sure are you that you are correct?

  3. IVs in Perception Experiments • Physical characteristics of stimuli: • Visual: size, shape, background, perspective. • Auditory: pitch, intensity, waveform (timbre), complexity, relation of sounds to each other. • Time course – brief presentation. • Sensory degradation or deprivation.

  4. Control Variables • Physical aspects of the stimuli that are not being investigated (manipulated). • Emotional and motivational aspects of the task. • Hungry people see food-related objects. • Decision aspects of the task.

  5. Verbal Reports • Since we cannot know the phenomenological experience of a person viewing a stimulus, what do verbal reports mean? • A verbal report is meaningful if there is a relationship between it and the characteristics of the preceding perceptual event. • Most people respond in similar ways to the same stimuli. • Because a relationship exists, we can infer the phenomenology from the verbal report given.

  6. Redefining Perception • If perception is the interpretation of sensation, how can phenomena such as “blindsight” occur? • Blindsight – visual capacity in a blind spot while there is no awareness of perception. • Someone’s performance shows they can “see” but they report not seeing anything. • D.B.’s scotoma (blind spot) was related to brain injury to the system that identifies objects.

  7. Can You Learn in Your Sleep? • How about weight-loss during sleep? • Are teenagers being influenced by satanic verses hidden in rock & roll songs? • http://www.umich.edu/~onebook/pages/frames/legalF.html • Do “subliminal” pictures of hot buttered popcorn increase the likelihood that people will eat popcorn in a movie theater?

  8. Perception Without Awareness? • Marcel (1983) used a primed Stroop task presented using a tachistoscope. • A prime word (a color word or a neutral word) was presented, followed by a mask at: • 400 ms (aware condition) • A shorter interval allowing only 60% detection of the prime (unaware condition) • A color patch followed the mask. • Prime and patch were either congruent, incongruent, or neutral.

  9. Marcel (1983) Results • Regardless of whether subjects were aware or unaware of the prime, compared to control: • Faster responses on congruent trials • Slower responses on incongruent trials • Conclusion: meaning CAN be perceived without awareness • Conclusion: the prime’s meaning is processed mentally, despite subjects’ verbal reports that they never saw the prime.

  10. What is a Threshold? • Threshold -- an intensity value above which a person always perceives, and below which a person does not perceive. • Think of a door – the higher the threshold, the more difficult it is to enter a room • Threshold and sensitivity are inversely related. • Higher threshold means less detection. • Lower threshold means more detection.

  11. Cheesman and Merikle (1984) • Questioned Marcel’s results – different thresholds may be used by different cognitive processes: • Detection threshold • Verbal report threshold • The threshold for conscious awareness of words may be higher than for responding differentially to their meanings. • Marcel’s mask may have interfered with one threshold (consciousness) but not the other.

  12. Cheesman & Merikle’s Method • The prime-mask interval was set by forced-choice detection of the 4 color word primes at 25%, 55%, and 90% • Subjects said they couldn’t see prime in all three conditions (25%, 55%, 90%). • Otherwise, their method was similar to Marcel’s.

  13. Verbally unaware V. Aware

  14. Two Threshold Theory • Based on their findings, Cheesman & Merikle suggest that there exist two kinds of thresholds: • Objective threshold – where discriminative responding is at chance. • Subjective threshold – where responding is above chance but subjects report being unaware of the stimuli. • This defines the three regions.

  15. Cheesman & Merikle (1986) • Does unconscious processing differ from conscious processing? (Yes, it does) • Varied % of congruent trials (33 vs. 66) • Previous results: For conscious processing, the more congruent trials, the greater the difference between congruent/incongruent RTs • Subjects are biased to respond “congruent” because they know it’s the most frequent trial • Does this occur when they don’t know?

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