Introduction to Cognitive Psychology - Department of Psychological ...

Prof. Greg Francis 1/2/12Strange property!! As the target’sduration orluminanceincreases!!its persistencedecreasesNetworks!! Feedback isimportant!! Produces a persistingresponse!! DemonstrationInput from eyesPurdue UniversityPurdue UniversityExplanation!! Francis, Grossberg & Mingolla (1994)!! Something has to reset the network!!else it would keep “persisting” forever!! Two mechanisms!!(1) new inputs inhibit old responses!!(2) afterimages act as new inputs!! Note: afterimages get stronger as durationand luminance increase!Purdue University!! Offset of input fromExplanationthe eyes produces anafter response!!e.g., due tocompetition fromorthogonally tunedcells!! Offset responseinhibits persistingresponseInput from eyesPurdue University!! As the target’sduration orluminanceincreases!! the afterimageproduced at targetoffset increases instrength!! so there is strongerinhibition to breakthe feedback!! so the persistenceof the originalpercept decreasesExplanationPurdue UniversityWait a minute!! If visual percepts persist for over 100milliseconds, why doesn’t the world seemblurry?!!There should be smears of objects as theymove or as we move!! There must be something else preventingsuch blurring!!maskingPurdue UniversityPSY 200: Intro. to Cognitive Psychology 2