Expert Testimony: Perceiving

An eyewitness testifies based on perceiving under excellent or difficult circumstances.

Ralph Haber, Ph.D. provides expert testimony on factors that affect the accuracy of perception:

The best circumstances for good observation are under high light levels, close to the action, on a clear day, for sufficient time, and with no distractions.

Lighting Factors: In general, higher the light levels, the better able to perceive: accuracy of perceiving is sharply reduced in low light levels. Back-lighting negatively affects perception of facial features, as do shadows. If the witness is in bright light, it is much more difficult to see into dark places.

Distance Factors: Accuracy of perceiving details is reduced by greater distance between the witness and the action or object, with the effect greater at night.

Duration Factors: Very brief events are more difficult to see completely and accurately compared to longer ones, especially if there are distractions, or many people involved.

Weather Factors: All atmospheric effects (fog, snow, rain) reduce accuracy of perception, compared to clear atmospherics.

Perspective and Distraction Factors: Perception is less accurate if the witness is not oriented toward the action of the event as it occurs, is not looking in the right place, or is distracted by other events at the same time, or is focused on something else, such as gore, or a weapon.

An excellent general textbook on factors that affect the accuracy of perceiving is: Ralph Haber and Maurice Hershenson (1980) The Psychology of Visual Perception (2nd Edition). New York: Holt, Rinehart and Winston Publishers.

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