Figure 7 presents the mean percentage of successfully discriminated stimuli that were actually different (hereafter ‘hits’), and the percentage of false alarms, i.e. ‘different’ responses to (identical) AA stimuli. The false-alarm rate is roughly 20% across the entire stimulus continuum. This value can be seen as a bias for responding ‘different’. Generally, an increment of 0.25 ERB is discriminated above the 20% bias level, with the exception of the difference between stimulus steps 5 and 6. The discrimination function shows two local peaks. The first one is very large, and is located between stimulus steps 2 and 3. This peak obviously coincides with the stable category boundary found between ‘command’ and the non-command responses (whether binary or ternary). A much smaller second discrimination peak may be observed between stimulus steps 6 and 7, which location may well reflect the rather poorly defined category boundary between ‘continuation’ and ‘question’.
F igure 7. Percent ‘different’ judgments to nine identical stimulus pairs (false alarms) and eight pairs differing by one step (hits).
