Bernhard Treutwein

Improvements in measuring thresholds, or points on a psychometric function, have advanced the field of psychophysics in the last 30 years. The arrival of laboratory computers allowed the introduction of adaptive procedures, where the presentation of the next stimulus depends on previous responses of the subject. Unfortunately, these procedures present themselves in a bewildering variety, though some of them differ only slightly. Even someone familiar with several methods cannot easily name the differences, or decide which method would be best suited for a particular application. This review tries to illuminate the historical background of adaptive procedures, explain their differences and similarities, and provide criteria for choosing among the various techniques.

In case of multiple sclerosis the discrimination of double-pulses of light is a more sensitive test of local damage in the visual field than visual acuity and critical flicker fusion frequency (Galvin et al., 1976, 1977). The same technique is also a diagnostic tool for detecting glaucoma (Stelmach et al., 1986). Given these facts, it is surprising that the method of double-pulse resolution is rarely used in clinical vision research. This may be a consequence of the apparent contradictions between a number of studies on the foveal discrimination of double-pulses (Mahneke, 1958; Venables, 1963; Kietzman and Sutton, 1968; Boynton, 1972), as well as methodological problems. I tried to resolve the difficulties by measuring double-pulse resolution by means of an extended version of the paradigm of Stelmach et al. (1986). It allows the quasi-simultaneous measurement of double-pulse resolution at 9 locations in the visual field. I also employed an adaptive psychophysical procedure which provides a maximum likelihood estimate of the threshold parameter (Treutwein, 1989).