Academic journal article Memory & Cognition

On the Immunity of Perceptual Implicit Memory to Manipulations of Attention

Academic journal article Memory & Cognition

On the Immunity of Perceptual Implicit Memory to Manipulations of Attention

Article excerpt

In four experiments, we examined the effect of manipulating study phase attention in a Stroop task on the extent of repetition priming in the lexical decision task (LDT). Experiment 1 replicated the immunity of the LDT to division of attention reported by Szymanski and MacLeod (1996), using a standard Stroop configuration. Response times to previously encountered words were identical regardless of whether the participants were required to read the words or name the color in which they were presented. Experiment 2 demonstrated that implementing the Stroop manipulation across separate visual objects reduced but did not eliminate priming of unattended words, provided the words remained in the attended region of the stimulus display. When this constraint was removed in Experiment 3, priming of unattended words disappeared. Experiment 4 demonstrated statistically equivalent priming for attended and unattended words when the Stroop manipulation remained in the same visual object but attention was directed to a single letter of the word. In all four experiments, the Stroop manipulation had a clear effect on recognition. These results qualify claims that the LDT might be immune to manipulations of study phase attention and suggest that the LDT has a lower threshold level of attention at encoding than do other standard implicit tests of memory.

Attention during the encoding of information has a substantial impact on the subsequent recall or recognition of that information. In these explicit tests of memory, which encourage effortful retrieval, there is a clear advantage for items that are attended at study over those that are ignored (e.g., Craik & Lockhart, 1972). In contrast, implicit tests of memory, in which retrieval may be unintentional, display less consistent effects of study phase attention: Sometimes there is an advantage for attended items (e.g., Mulligan, 2003; Mulligan & Hornstein, 2000; Rajaram, Srinivas, & Travers, 2001; Stone, Ladd, Vaidya, & Gabrieli, 1998); sometimes no effect of attention is found (e.g., Jacoby, Wcloshyn, & Kelley, 1989; Mulligan & Hartman, 1996; Parkin, Reid, & Russo, 1990; Szymanski & MacLeod, 1996); and sometimes implicit tests show effects of attention that are absent in explicit tests (e.g., Kinoshita, 1995; Merikle & Reingold, 1991; but see Berry, Shanks, & Henson, 2006).

One clear impediment to resolving the issue of how attention affects implicit memory is the variety of methods and measures used to index memory. The inconsistent effects of attentional manipulations on implicit memory may, in large part, be attributable to the different methods of dividing attention and measuring memory (Stone, Ladd, & Gabrieli, 2000). The implicit memory literature distinguishes between implicit memory tasks according to whether they require conceptual or perceptual processing at retrieval (e.g., Blaxton, 1989), and this distinction appears to capture much of the variability in outcomes. Conceptual priming tasks, such as category exemplar production and free association, are more sensitive to divided attention at encoding (e.g., Gabrieli et al., 1999; Light, Prull, La Voie, & Healy, 2000; Mulligan & Hartman, 1996) than are perceptual priming tasks, such as word fragment completion (e.g., Mulligan & Hartman, 1996), perceptual identification (e.g., Schmitter-Edgecombe, 1996), and lexical decision (e.g., Kellogg, Newcombe, Kammer, & Schmitt, 1996). But, as was noted above, even within the class of perceptual implicit memory tests, there is evidence both for complete immunity to attentional manipulations at encoding (e.g., Jacoby et al., 1989; Parkin et al., 1990; Szymanski & MacLeod, 1996) and for attentional impairments that mirror those found in explicit memory (Crabb & Dark, 1999; Mulligan, 2003; Rajaram et al., 2001; Stone et al., 1998).

A plausible hypothesis tested by Rajaram et al. (2001) is that attentional manipulations affect perceptual implicit memory tests (stem completion, fragment completion, perceptual identification) when the method for dividing attention interferes with the perceptual analysis of the word during study. …

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