F i g. 2 . Racognitton t hre shol ds for forward and backward mask ing as a fun ction of masking sti muli and interstimulus in terv al s . circular pattern (visual angle = 65'). The masking stimuli, which were al so ne gative prints, transmitted an equal amount of luminance flux; their luminance was 4.2 ft L . The duration of the letters and masking stimuli was held constant at 2 msec .AteachISlemployed (5, 30 , 60 , and 100 msec .) the intensity of the letter was increased in 0.1 log unit steps by the useof Kodak neutral density filters until Ss correctly identified th e letter. Stimuli were presented to the dark adapted eye.Half of each session was devoted to FM, and the other half to BM, with the order reversed each day . Masking stimuli were r andomized in blocks of 8, ISIs in blocks of 4, with thresholds for 2 letters taken at each lSI per session . Over a period of 10 sessions 20 thresholds were obtained for each of the 24 cond itions.
ResultsThe results for two Ss, illustrated in Fig. 2, show the following; (1) The amount of interference is greater with FM than with BM. Anal ysis of variance showed this difference to be significant beyond the .01 level. The data indicate that the differences are slight at the short ISIs but in crease with increasing lSI. The interaction between lSI and masking order was also significant for
AbstractDifferences between forward and backward masking were studied by employing a disk, a r ing anda pattern as masking stimuli and letters a s test stimuli. The results show th at interferen ce is greater in forward than in backward masking. Interferen ce wa s found to decrease monotonically with increa sing interstimulus intervals (lSI) in all cases. Of the three masking stimuli, the ring produced the le ast interference and the pattern the most. Problem