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# class+24+lecture+_review_ - Sensation and Perception Class...

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Sensation and Perception Class XXIV: Review

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Please complete the Student Instructional Survey on the Sakai site! If you missed a midterm, the make up exam is May 3 at 12 PM in Psych 333.
Warning about this review session: The exam will include many things that are NOT covered today, but many of the things covered today WILL be on the final exam.

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Adaptation: A reduction in response caused by prior or continuing stimulation Sensory transducer: A receptor that converts physical energy from the environment into neural energy Psychophysics: the quantitative relationship between the physical stimulus (R) and its corresponding sensation (S). JND (just noticeable difference): The smallest detectable difference between two stimuli, or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus.
Psychophysics Weber’s Law: The size of the JND for a stimulus is a constant proportion of the size of the stimulus. Expressed mathematically: S is the sensation R is the physical stimulus intensity k is a constant that depends on the sensory modality (d) means the change in following variable (remember dx/dt from calculus?) Weber’s law: dS = k (dR/R)

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Psychophysics Fechner’s law: S= k ln(R) This equation says that the perceived intensity of the stimulus (i.e. the sensation, S) increases as a logarithmic function of the magnitude of the physical stimulus (R). You can think of a logarithmic function as one that gives diminishing returns - moving to larger physical stimuli increases the perceived intensity LESS than you might expect.
The Dawn of Psychophysics Stevens’ Law: A principle describing the relationship between stimulus magnitude and resulting sensation magnitude, such that the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent Stevens’ law: S= k Rb where k and b are modality-specific constants. This reduces to Fechner’s law when the exponent is less than one (e.g. brightness, loudness estimates), but allows for special cases in other modalities that don’t follow Fechner’s law (e.g. electric shock, short distances).

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The Dawn of Psychophysics Thresholds Sensory thresholds are not all-or-none. When you get close to the limit of what you can detect, sometimes you detect the stimulus and sometimes you don’t. We therefore define thresholds statistically. Absolute threshold : Minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time Recognition threshold : The minimum amount of stimulation necessary for a person to identify a stimulus correctly 50% of the time.
The Dawn of Psychophysics Psychophysical methods for threshold measurement: Method of constant stimuli: Many stimuli, ranging from rarely to almost always perceivable, are presented one at a time. (Disadvantage: needs many, many trials.) Method of limits: The magnitude of a single stimulus or the difference between two stimuli is varied incrementally until

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class+24+lecture+_review_ - Sensation and Perception Class...

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