In a review of the detection literature, Smith (
2000) pointed out that signal enhancement is typically reported only when stimuli are backwardly masked; when no masks are used, signal enhancement is not usually found. Studies investigating the effects of covert attention on detection using backwardly masked stimuli by Bashinski and Bacharach (
1980), Downing (
1988), Hawkins et al. (
1990), Luck et al. (
1994), Müller and Humphreys (
1991), and Smith (
1998) found evidence of signal enhancement; studies by Bonnel, Stein, and Bertucci (
1992), Davis, Kramer, and Graham (
1983), Foley and Schwarz (
1998), Graham, Kramer, and Haber (
1985), Lee, Koch, and Braun (
1997), Müller and Findlay (
1987), and Palmer, Ames, and Lindsey (
1993) using unmasked stimuli found no evidence of signal enhancement. Consistent with this, in a series of detection studies by Smith et al. using displays that controlled the effects of uncertainty, signal enhancement was found with masked but not unmasked stimuli (Smith,
2000; Smith, Ratcliff, & Wolfgang,
2004; Smith & Wolfgang,
2004; Smith, Wolfgang, & Sinclair,
2004). However, two recent studies by Carrasco et al. reported signal enhancement in cued detection tasks in which no backward masks were used (Cameron, Tai, & Carrasco,
2002, ±15° task; Carrasco, Penpeci-Talgar, & Eckstein,
2000).