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2 – Object Recognition A visual scene consists of objects: creatures, faces, enemies, food Object recognition is complex – not merely a comparison of stimulus.

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Presentation on theme: "2 – Object Recognition A visual scene consists of objects: creatures, faces, enemies, food Object recognition is complex – not merely a comparison of stimulus."— Presentation transcript:

1 2 – Object Recognition A visual scene consists of objects: creatures, faces, enemies, food Object recognition is complex – not merely a comparison of stimulus to memory. Several factors affect object recognition: Light and Shadow

2 Motion can facilitate object recognition. In fact, some objects are recognizable only when in motion. Examples (Donald Hoffman) (Michael Bach) (Nicholas Troje) (G. Johansson, 1973)

3 Motion can also inhibit object recognition. apparent motion rapid sequence of still objects misperceived as one moving object Examples animation neon lights Animations (Wertheimer, 1912)

4 Object recognition can be impeded by figure-ground confusion

5 Context Effects is read as “THE CAT” even though “H” and “A” are identical. context effect perception of stimulus is altered by surrounding stimuli Thus, perception depends on bottom-up processes guided by stimulus looks like A or H top-down processes guided by knowledge should be A or O  must be A.

6 More examples EGG FUN Poelpe dsilkie radeing snetenecs wtih rarergaend lteerts. Can you read this handwritten word?


8 Context effects allow perception of a missing stimulus. Example (from a magazine ad) L ke y ur b ain, the n w L nd Rov r autom tic ly adj sts to anyth ng. Context effects can create perceptual errors. Example Who is standing behind Bill Clinton?

9 Another context effect Experiment On each trial, S saw underlined letter that appeared alone or as part of word. K DARK S was asked to read the underlined letter. All letters appeared simultaneously and disappeared simultaneously. Letters presented so briefly that identification was hard. Result: Accuracy was greater when letter appeared as part of a word. (Reicher, 1969)

10 Another context effect Experiment Ss listened to audiotape of sentences with missing sound. The eel was on the axle. The eel was on the shoe. After each sentence, Ss repeated what they heard. Results: Ss unknowingly “replaced” the missing sound. The wheel was on the axle. The heel was on the shoe. (Warren, 1970)

11 Seeing-Hearing Context Effect Experiment Ss viewed video of person saying FA FAFAFA while listening to audio of BABABABA Then Ss were asked to repeat what they heard. Modal response: FAFAFAFA That is, they believe they “heard” what they actually saw, not what they actually heard. Video (3:39) (McGurk & MacDonald, 1976)

12 Another seeing-hearing context effect Demo Experiment Ss viewed video of two disks. Each disk moved along a linear path at constant speed. The disks simultaneously reached the center point. At that moment, Ss heard a “clink” on some trials. Results: Modal Self-Report No ClinkDisks pass through each other ClinkDisks collide. (e.g., Metzger, 1934)

13 Subliminal Perception Prototypical Experiment S saw briefly presented word, followed by mask S cannot identify word. Later, S was asked to choose the word from a list Results: Accuracy slightly greater than chance Conclusion Under precisely controlled conditions, subliminal perception is a real phenomenon (e.g., Cheesman & Merikle, 1984)

14 Subliminal Perception Outside the Lab Experiment Ss were asked to listen to music audiotapes with embedded message. ½ Ss given tape labeled “Memory” and were told that message improves memory. ½ Ss given tape labeled “Self-Esteem” and were told that message boosts self-esteem. Deception: For half of the tapes of each kind, the label did not match the message. One month later, Ss returned for tests. Results Type of message (memory vs. self-esteem) had no effect on Ss memory or self-esteem. Yet some Ss reported improvement that matched label, not message (placebo effect). Conclusion No subliminal perception (Greenwald, Spangenberg, Pratkanis, & Eskenazi, 1991)

15 agnosia disorder in which patients cannot assign meaning to visually-perceived object But vision and visual perception are normal Case Study – Doctor showed patient a bell Doctor PatientImplication What is this? I don’t know. What is it for? I don’t know. agnosia  word finding difficulty Describe it.It’s metallic - about 15 cm tall. agnosia  vision problem [Rings bell.] Oh, that’s a bell. agnosia  auditory issue What is it for? It alerts people. (Ghadiali, 2004)

16 Another agnosia case study Doctor showed patient a rose Doctor Patient What is this? “A convoluted red form with a linear green attachment.” Smell it. “It’s a rose.” “When leaving, the patient looked around for his hat. He reached out his hand and took hold of his wife’s head and tried to lift it.” (Patient Dr. P, Sacks, 1987)

17 Another agnosia case study Patient could not identify objects (left) but could copy objects (right). (Patient L.H., Farah, 2004)

18 Diagnosis of Agnosia Patients asked to identify objects depicted in photos (Images part of the Birmingham Object Recognition Battery) Case study video (1:22)

19 Faces Are Special Faces are remarkably similar (when matched for gender and skin color) Yet we can distinguish between hundreds of faces. Hypothesis: mind has mechanism (brain region?) devoted to face recognition. This “faces-are-special hypothesis” is supported by several kinds of data.

20 Thatcher illusion distortion not noticed when face is inverted implication: face perception is specially suited for upright faces (Thompson, 1980)

21 Demo – Who are they?

22 Inverted Face Recognition Experiment Ss saw photos of famous faces and common objects. Photos were upright or inverted. Ss tried to identify face (e.g., Reagan) or object (e.g., house) Accuracy and response time measured. Results ObjectsFaces UprightGoodGood InvertedFairly Good Bad (Yin, 1969)

23 prosopagnosiainability to recognize familiar face (but patients know it’s a face) Patients with prosopagnosia cannot recognize famous faces like these

24 prosopagnosia provides further evidence that faces are special recognize objectsrecognize faces some patients yesno other patients noyes Example “A sheep farmer with prosopagnosia failed a facial recognition test in which he had to identify a familiar face from unfamiliar faces. In contrast, he was able to recognize familiar and unfamiliar sheep.” (Ghadiali, 2004) (De Renzi, 1986; Farah, 1992)

25 Prosopagnosia test – Do you recognize these people?

26 Another Prosopagnosia Test All 3 top row photos depict the same man. Can you spot that man in the bottom row? courtesy of Ken Nakayama

27 In rare cases, prosopagnosia patients cannot recognize themselves in a mirror. (Farah, 1992) Yet patients can look at face photo and identify facial expression of emotion. (e.g., Duchaine et al. 2003)

28 prosopagnosia experiment Patient LF and 2 healthy controls looked at 10 famous face photos While looking at each face, S heard five names (15 s each). During this period, E measured skin conductance resistance (measure of emotion) Then, S was asked to choose the correct name. LFcontrols % of faces for which correct name was chosen 20% (chance)100% % of faces with highest SCR for correct name60% 80% Conclusion. Patient recognized face at some level outside his awareness. (Not all patients with prosopagnosia show this covert recognition.) (Bauer, 1984)

29 Prosopagnosia demo courtesy of the Exploratorium

30 Case Study Dr. S (a professor who suffered a stroke) Usually unable to recognize colleagues until they speak. IQ = 147 (Temple, 1992) Videos Patient Terry (3:31) 60 minutes 18 March 2012 part 1 (12:45) British tutorial (3:09)

31 Brain Games DVD - Perception (about 45 minutes – start at 1:54) The End

32 CAT analog problem bottom-uptop-downpercept THE CATH AHH HIS NAME IS BOBBRP B Rambiguity

33 Demo Two words will appear briefly in the box. Read them. Note to instructor: hit “Enter” twice in rapid succession.

34 Object recognition is sometimes aided by light and shadow. Example. Which dimples are raised? Why? Light usually shines from above. (image from O’Reilly

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