An explicit no response instead of time-out in automated visual-field testing

Background: To evaluate the effect of response-acquisition technique on psy chometric performance in visual-field testing, the conventional one-button yes/time-out method was compared with a two-button yes/no method for respon ding whether or not the stimulus was detected. There are a number of situat ions in which the single-button technique leads to ambiguous results. In th is study, we thus expected the yes/no method to reduce tendencies towards h abituation and automatic responding. Our hypothesis was that the two-button technique could reduce the rate of erroneous responses. Methods: Luminance -difference sensitivity for bright stimuli (32 ') on a photopic background was evaluated at 26 locations within the central visual field (30 degrees) using a specially equalised video display unit and a modified 4/2-dB stairc ase strategy (six reversals, maximum-likelihood threshold estimation). Sixt y-one ophthalmologically normal subjects (aged 20-30 years) were examined t wice with each method. Results: Mean sensitivities with the two-button yes/ no method were found to be, on average, 0.13 dB above those measured with t he one-button yes/time-out technique - a difference without clinical releva nce. Within-subject variability did not differ between the two methods. How ever, the less intuitive two-button yes/no method had a slightly higher nu mber of false responses in catch trials. Conclusion: Compared to the conven tional one-button yes/time-out method, the two-button yes/no method in norm al young subjects thus showed little difference in mean sensitivities and e quivalent within-subject variabilities. Concerning our initial hypothesis, the yes/no method is of somewhat higher complexity and is not able to reduc e the rate of erroneous responses. The one-button yes/time-out method fared a little better in error rate. In summary, the yes/no method is an alterna tive and additional possibility of response acquisition in visual-field tes ting, which is worthy of being tested in a clinical study with elderly subj ects.