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Spectral Masking.docx

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Department
Psychology
Course
PSYCH 3A03
Professor
Paul Faure
Semester
Fall

Description
November 15 , 2013 Psych 3A03: Audition Spectral Masking Differential Sensitivity - Stimulus thresholds define the ranges of detection for parameters of acoustic signals (e.g. frequency, intensity, phase, etc.) - Thresholds do not capture a subjects sensitivity to changes in a stimulus parameter - Psychophysicists also interested in measuring the smallest difference between physical stimuli that will just barely cause a difference in sensation (just noticeable difference) - How does perception scale with changes in stimulus modality and magnitude? - 2 famous psychologists looked at the question of how differences in stimulus intensity (magnitude) map on to perception Ernst Heinrich Weber - Devised method for measuring the existence of internal (mental) events; formulated the theory of signs (Lokalzeichentheorie); with his brother he studied acoustics and wave motion st - Discovered psychology’s 1 empirical constant – weber fraction. This concept uses the awareness of a difference in sensation to measure a difference in sensation - Weber fraction: the increase in stimulus intensity necessary to produce an increase in sensation is not a fixed quantity but is a constant proportion of the smaller intensity - - Through experimentation, Weber found that the smallest intensity difference (ΔI) between 2 nearly identical stimuli that a person could just detect was proportional to intensity of the smaller stimulus (I) - Size difference threshold between nearly identical stimuli (I and [I + ΔI]) is a constant proportion of magnitude of the smaller stimulus (I) Gustav Theodor Fechner - Studied anatomy under E.H. Weber - Developed first theory of hypothesis testing; technical foundations for descriptive statistics; ideas about consciousness; first measurement of a features of the mind - His book Element der Psychophysik described methods for quantifying the relationships between sensory stimuli and perception - Father of modern psychophysics - Research on the accuracy of perceptual representations of physical stimuli considered to be the bedrock of early experimental psychology - The realization that the relationships between stimulus events and mental events might be reducible to simple laws occurred to Fechner while lying in bed on morning of October 22 , 1850d - Fechner was so impressed by Weber’s Law that he belied it was the basis for a general quantitative relationship between the magnitude - Weber’s law: smallest difference between 2 nearly identical stimuli that a person can detect is proportional to the magnitude of the smaller stimulus - Fechner termed this perceptual difference threshold as a just noticeable difference threshold - Relate quantity of just noticeable difference vs. quantity of stimulus change - JND is a psychological entity expressed in units of stimulus magnitude - JND scale: equal sensation intervals - Fechner’s law: magnitude of sensory response (R) increase with logarithm of stimulus intensity (S) above stimulus threshold (S ): R 0 klogS Example of the Weber-Fechner Law - Weights: 100g vs. 100g + 5g; JND – 5g – if we double the masses JND – 10g as it is a constant proportion - Person detects difference between 1 & 2lb weight - Cannot discriminate 101 lbs from 102 lbs even though same absolute difference - Can discrimination 1.0lbs from 1.1lbs, and can discriminate 100lbs from 110lbs; these all have the same relative difference - Just noticeable difference (JND) = 0.1 or 10% Reasoning of Weber-Fechner Law - Weber’s law: smallest difference between 2 nearly identical stimuli that a person can detect is proportional to the magnitude of the smaller stimulus - Fechner termed this perceptual difference threshold as a just noticeable difference threshold - JND is a psychological expressed in units of stimulus magnitude - JND scale: equal sensation intervals - Fechner’s Law: magnitude of sensory response (R) increases with logarithm of stimulus intensity (S) above
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