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Eyewitness testimony: Sensation & Perception

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Presentation on theme: "Eyewitness testimony: Sensation & Perception"— Presentation transcript:

1 Eyewitness testimony: Sensation & Perception
Seeing is believing? Sensation is based on physiological parameters that differs from person to person Color blindness, acuity, threshold, saturation, etc. Hormones, level of electrolytes, teratogens (eg. Drugs) Environmental factors such as background also affect sensation Background colors and patterns Much of the same confounding factors apply to hearing and other senses

2 Eyewitness testimony: Sensation & Perception
Perception is the analysis by the brain of sensory input It is NOT a one-to-one correlation between input and final perception Perception is an active re-creation of what is an approximation of the input During re-creation the brain makes assumptions and also makes errors: Illusions Hallucinations

3 Eyewitness testimony: Sensation & Perception
Factors affecting perception: Past experience (Helmholtz’ glasses) Orienting reaction (basis for rapid changing images on TV) Gestalten: Closure Proximity Similarity Pregnanz Figure-ground attention

4 Eyewitness testimony: Sensation & Perception
Factors affecting perception continued: Personality Motivation Culture Social influences such as conformity: Asch experiment The following slides contain examples of the material presented above

5 Eyewitness testimony: Sensation & Perception
Perceptual analysis slowed down to demonstrate the process

6 Eyewitness testimony: Sensation & Perception
All the color palettes are the same

7 Eyewitness testimony: Sensation & Perception
Muller-Lyer illusion

8 Eyewitness testimony: Sensation & Perception
Or 2 faces A vase A figure-ground example

9 Eyewitness testimony: Sensation & Perception
Rabbit or bird: a figure-ground example

10 Eyewitness testimony: Sensation & Perception
We see what we think should be seen

11 Eyewitness testimony: Sensation & Perception
Perceptual error leads to impossible figures

12 Eyewitness testimony: Sensation & Perception
Perceptual error creates “facts” (spirals) where none exist

13 Eyewitness testimony: Memory
Memory is a construction and reconstruction process: rehearsal Selective attention Short-term memory Sensory memory Long-term memory Sensory input Loss of information Forgetting and interference

14 Eyewitness testimony: memory (2)
Sensory memory is part of the perception process During the analysis of sensory data, selective attention determines which items will be retained for further memory processing Ongoing events, personality, cultural biases, etc. will affect selective attention Short-term memory is active and limited It requires active rehearsal or information is lost at 30 seconds It is limited to 7±2 bits of information When overloaded: Proactive interference: new info displaces old Retroactive interference: old info displaces new info

15 Eyewitness testimony: memory (3)
Transfer to long term memory requires encoding of data (consolidation) multitude of factors affect what info will be transferred Yerkes-Dodson Law shows that info stored at low or high arousal states will be less accurate that those stored at moderate levels of arousal Social factors such as the need to obey, social facilitation, and cognitive dissonance will affect memory reconstruction Different aspects of memory stored in different ways and locations Interactive memories may merge Remembering requires reconstruction of the encoded LTM and retrieval back to STM Same factors that affected storage will affect retrieval Retrieval mechanism itself may be a factor Cues and memory retrieval: Retrieval without cues (recall) is difficult but subject has high confidence Retrieval with cues (recognition) is easier but subject has low confidence

16 Eyewitness testimony: memory (4)
As a result of memory factors, eyewitness testimony is prone to error: If the witness is asked to describe a suspect, the subject will be sure the description is accurate even if it is not If the subject is shown a series of pictures and asked to identify the suspect, the subject may be right but inconsistent Selective attention factors are shown when we examine how subjects recognize faces: We focus more on the details of faces that have high valence to us…members of our own cultural group, or faces of cultural groups we fear the most We focus more on upper facial features than lower facial features, hence changes in upper facial features affect our perceptions and memory more than other features as seen by the next slide:

17 Eyewitness testimony: conclusions

18 Eyewitness testimony: Conclusions
Most eyewitnesses are in a state of high arousal during the time they witness the event, during interrogation, and during testimony. The Yerkes-Dodson law predicts major errors. Cognitive dissonance and social facilitation, predicts that once a witness has provided their evidence, there will be a “hardening” of memory Hypnosis, which is a high state of suggestibility, is most prone to the problems of reliability and validity of remembering and not acceptable as proof (problems of recovered memories using hypnosis and age regression hypnosis) Children, who have less sophisticated mental structures tend to be more accurate when they describe events they participated in without adult prompting, but are very inaccurate when prompted by adults or when details are missing (closure Gestalt): Eg: if the suspect is missing in a lineup, children are more likely to identify someone else

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