Perception • Active process • Involves selection, organization and ...

Perception• Active process• Involves selection, organization andinterpretation of sensory input• rapid, largely unconscious• Requires special techniques, unusualcircumstances to reveal• Factors influencing organization andinterpretation of sensory input:

1. Past experience.

• Factors influencing your perception• Past experience with cows in general• Your experience with the drawing>

2. Gestalt organizing principles (tendencies)• Gestalt psychologists:• Recognized- we seek meaning, pattern,structure• Asked: Any basic tendencies governinghow we organize sensory input?• Found several

e.g., Continuity• What do you see?• How many lines?• We have preference for continuous figures(also illustrates “Closure”)

e.g., Proximity• Describe what you see• Not just dots (we organize); and not rows• Principle: things which are closer togetherwill be seen as belonging together

e.g., ** figure-ground separation **• [describe]• “Figure” stands out, seen in more detail• rest seen in less detail, recedes intobackground• (May not even be noticed)

Figure-ground reversals

3. Perceptual set• Experiment [instructions]>

[instructions]Group B>.

(check results….)

• Perceptual set (= expectation) caninfluence what we perceive• “tunes” our perception• Plays significant role in perception ofpain1) Anticipation of pain experiment[describe]2 groups of subjects (experimental and control groups)All Ss told: “measuring physiological effects of differenttypes of music…”Experimental group Ss were given additional info: “By theway….”

• Experiment proceeds….music played• Over next 20 min., Ss (in both groups) do receive a few mildelectric shocks• At end: Ss asked for comments• Then fill out questionnaire• Results:• Asked to rate severity of shocks• Ss in experimental group:• More likely to notice, rated shocks as more severe• Expectations influence perception of pain• Purely psychological?…

• Porro et al. (2002) fMRI study: scanned Ssanticipating injection in specific foot• Heightened activity (though less intense), duringwaiting period, in regions of brain activatedwhen actual pain experiencedAnterior cingulate cortex (ACC) and insulasomatosensory projection area (contralateral)• “Priming effect”: cognitive activity sensitizing.sensory/affective regions

2) Placebo Effect• If expectation of pain can increase pain intensity,• how might expectation of pain reduction influenceperception?• e.g., following surgery [describe scenario where placebo might be given]• Experimental results• E.g., 85% of Ss given placebo for relief of paincaused by Herpes (cold sores or genital sores)reported pain reduction• E.g., 56% of patients given sham treatment(small skin incision) for angina (heart pain)reported significant pain reduction• On average, 33% of Ss in placebo pain studiesreport pain reduction

Why the high responsiveness to expectationof pain relief?• Evidence that expectation of pain relief activatesmu-opioid neurotransmitter system (“endorphins”)Red & orangeindicate regions ofheightened muopioidactivitywhen P reportspositive effect ofplaceboZubieta et al - Placebo Effects Mediated by Endogenous Opioid Activity on µ-Opioid Receptors (2005)