Classical method
1. method of limit
2. method of adjustment
3. method of constant stimuli
4. adaptive method
5. signal detection theory
6. identification experiment
Threshold
1. Detection threshold (Absolute threshold)
2. Discrimination threshold (difference threshold)
Absolute threshold:
절대역 = 사람이 자극을 알아차리는데 필요한 최소한의 자극강도를 말한다.
절대역 이하의 자극은 역학자극이라고 함
Method of limit : 한계법 자극의 강도를 약한수준 에서 조금씩 순차적으로 증가 관찰자로 하여금 자극을 탐지할 수 있는지 답하게 하는 방법 Yes, No의 중간을 절대역으로 정함.
Method of adjustment : 조정법 관찰자가 자극을 탐지할 수 있다고 말할 때 까지 관찰자, 실험자가 직접강도를 변화 시킴
Method of costant stimuli : 항상 자극법 실험자가 자극을 관찰자에게 제시한다는 점에서 한계법과 유사 , 다른점은 자극을 무작위적으로 제시한다는 점이 다름.
항상자극법 정확하지만 시간 많이걸림 반면 조정법은 시간은 적게 걸리지만 정확하지 않음 .
Adaptive Method: Staircase: 한계법과 유사하지만 결정이 변경하는 언제든지 방향을 달리함
threshold 값이 예측에 보다 효과적
Signal Detection Theory: 정신물리학 이론, 관찰자의 반응을 계산한다.
Method
Measures absolute and difference thresholds
• An initial stimulus intensity must begin far below/above the upper/lower limit for an ascending or a descending series
• Procedure – Present subjects with ascending and descending stimulus series and ask “is a comparison is greater or smaller than the reference?”
– Start with a level that you think the participant will feel/see/hear
– If the participant feel/see/hear that one, then present a lower level
– Continue until the participant says he/she can’s feel/see/hear the stimulus
– Repeat with randomized ascending and descending series.
– The more repetitions provide the more accurate thresholds but inefficient. Thus, the number should be determined based on the type of experiments.
Method of limits (cont.)
• AL (Absolute Threshold)
– A series of ascending or descending steps are presented until it reaches the upper limit or the lower limit
– On each trial the subject responds whether she/he can detect the presented stimulus (e.g. Yes or No) – Ascending and descending series are done in alternation several times
– Threshold for the series is estimated as the midpoint between the stimulus intensities for the last YES response and the first NO response 10 Method of limits (cont.)
• DL (Discrimination Threshold)
– The reference stimulus is fixed and the subject must report whether the test stimulus is “equal or greater” for an asymmetric design, or “greater or less” for a symmetric design
– Ascending & descending series are done in alternation several times
– Threshold for the series is estimated as the average/a standard deviation of the transition points in the asymmetric design/the symmetric design