Selection ofshock level. Shocks were 200ms duration and between 1.0 and 2.0 mA instrength. Each subjectset her own shock level. Each subject was instructed to choose a level of shock that was uncomfortable but not painful. Each was given a sample shock of 2.0 mA. If thiswas too strong, the levelwas decreased and another samplewasgiven. Shock levelwas then increasedor decreased inresponse to the subject's reactions untilan uncomfortable but not painful level was found or until the level reached 1.0 mA. We were concerned that shock levels below 1.0 mA would be too weak to produce conditioningor might result in rapid habituation. Accordingly, we decided to exclude subjects who selected shock levels below 1.0 mA.

電流としては、商用周波数で0.5mAが人体に感じる最小の電流と言われており、10mAを超える電流では筋肉の随意運動が不能となる。電流密度が高く通電部組織の発熱量が多い場合には、ジュール熱による火傷や組織壊死を生ずる場合もある。人体の器官のうち心臓は特に電流に敏感であり、100μA(0.1mA)を超える電流が心臓を通過すると心室細動、心停止を起こし死に至る危険性があるとされている。