Direct Subjective Assessments

S. Smith Stevens, countered this view saying that

• the accuracy of discrimination of a stimulus (JND) isn't necessarily related to the overall perceived magnitude of a stimulus;
• just as an accumulation of error in the position of a needle on a voltmeter doesn't necessarily yield voltage, an accumulation of JNDs doesn't necessarily have anything to do with perceived magnitude;
• believed difference in stimuli should be measured by acquiring direct subjective assessments:
• e.g., present a tone and inform subject that the tone is numbered 30 for loudness;
  • if a subsequent tone seems twice as loud, subject should label it 60;
  • if half as loud, label 15;