DIFFERENTIAL THRESHOLD OF LENGTH AND RESPONSE CRITERION FOR INSPECTING IRREGULAR OBJECTS

This research investigated human visual sensitivity and bias in inspec ting irregular objects. A preliminary study was conducted using the me thod of constants to determine the threshold value for judgment of siz e. A factorial experiment was conducted using payoffs, rate of defecti ve items, and detectability in the signal-detection theory as the fact ors. In total, eight experimental conditions were tested. 10 college s tudents were recruited as subjects. Each subject was asked to compare 40 teapot shapes to a standard teapot shape under eight experimental c onditions. Defective shapes were generated by lengthening the vertical dimension of a standard teapot shape by a factor of 1.01 and 1.04 for 'low' and 'high' detectability. The decision lime and responses of 'i dentical' or 'different' were collected under all experimental conditi ons. Analysis indicates that the decision-making strategy used to insp ect this irregular object was very close to maximizing the accuracy of decision-making by considering the rare of defective items. This resu lt is different from most research findings in signal-detection theory in which responses of human beings are similar to degraded Bayes opti mizers. The standard deviation of the signal distribution was about 1. 30 and 1.41 limes that of the noise distributions for 'low' and 'high' detectability.