William Prinzmetal, Virginia Long, James Leonhardt
Carrasco, Ling, and Read (2004) reported that involuntary attention increased perceived contrast. We replicated Carrasco et al. and then tested an alternative hypothesis: With stimuli near threshold, a peripheral cue biased observers to believe a stimulus had been presented in the cued location. Consistent with this hypothesis, the effect disappeared when we used higher-contrast stimuli. We further tested the guessing-bias hypothesis in three ways: (1) In a detection experiment, the cue affected bias, but did not increase d'; (2) when the cue followed the stimulus, we obtained the same results as when the cue preceded the stimulus; (3) in one experiment, some trials contained no stimulus, yet observers responded that the cued blank stimulus had higher contrast than the uncued blank stimulus...
October 2008: Perception & Psychophysics