Effects of cross-modal and intramodal division of attention on perceptual implicit memory

Not all identification tasks are born equal: testing the involvement of production processes in perceptual identification and lexical decision

The distinction between identification and production processes suggests that implicit memory should require more attention resources when there is a competition between alternative solutions during the test phase. The present two experiments assessed this hypothesis by examining the effects of divided attention (DA) at encoding on the high- and low-response-competition versions of perceptual identification (Experiment 1) and lexical decision (Experiment 2). In both experiments, words presented in the high-response-competition condition had many orthographic neighbours and at least one higher-frequency neighbour, whereas words presented in the low-response-competition condition had few orthographic neighbours and no higher-frequency neighbour. Consistent with the predictions of the identification/production distinction, Experiment 1 showed that DA reduced repetition priming in the high-, but not in the low-response-competition version of perceptual identification; in contrast, DA had comparable effects in the two versions of lexical decision (Experiments 2). These findings provide the first experimental evidence in support of the hypothesis that perceptual identification, a task nominally based on identification processes, might involve a substantive production component.

Effects of Divided Attention at Retrieval on Conceptual Implicit Memory

This study investigated whether conceptual implicit memory is sensitive to process-specific interference at the time of retrieval. Participants performed the implicit memory test of category exemplar generation (CEG; Experiments 1 and 3), or the matched explicit memory test of category-cued recall (Experiment 2), both of which are conceptually driven memory tasks, under one of two divided attention (DA) conditions in which participants simultaneously performed a distracting task. The distracting task was either syllable judgments (dissimilar processes), or semantic judgments (similar processes) on unrelated words. Compared to full attention (FA) in which no distracting task was performed, DA had no effect on CEG priming overall, but reduced category-cued recall similarly regardless of distractor task. Analyses of distractor task performance also revealed differences between implicit and explicit memory retrieval. The evidence suggests that, whereas explicit memory retrieval requires attentional resources and is disrupted by semantic and phonological distracting tasks, conceptual implicit memory is automatic and unaffected even when distractor and memory tasks involve similar processes.

Attention and implicit memory

The distinction between identification and production priming assumes that tasks based on production processes involve two distinct stages: the activation of multiple solutions and the following selection of a final response. Previous research demonstrated that divided attention reduced production but not identification priming. However, an unresolved issue concerns whether the activation of candidate solutions is sufficient to account for the enhanced request of attentional resources, independently from the contribution of selection processes. The present paper investigated this question by using a version of the lexical decision task (LDT) in which the target words had either many or few orthographic neighbors. Two experiments showed that the effects of divided and selective attention were equivalent in both conditions, suggesting that the inclusion of a process of generation of multiple solutions in the LDT is not sufficient to increase the amount of cognitive resources needed to achieve full priming to the levels of production tasks.

Effects of dividing attention during encoding on perceptual priming of unfamiliar visual objects

According to the distractor-selection hypothesis (Mulligan, 2003), dividing attention during encoding reduces perceptual priming when responses to non-critical (i.e., distractor) stimuli are selected frequently and simultaneously with critical stimulus encoding. Because direct support for this hypothesis comes exclusively from studies using familiar word stimuli, the present study tested whether the predictions of the distractor-selection hypothesis extend to perceptual priming of unfamiliar visual objects using the possible/impossible object decision test. Consistent with the distractor-selection hypothesis, Experiments 1 and 2 found no reduction in priming when the non-critical stimuli were presented infrequently and non-synchronously with the critical target stimuli, even though explicit recognition memory was reduced. In Experiment 3, non-critical stimuli were presented frequently and simultaneously during encoding of critical stimuli; however, no decrement in priming was detected, even when encoding time was reduced. These results suggest that priming in the possible/impossible object decision test is relatively immune to reductions in central attention and that not all aspects of the distractor-selection hypothesis generalise to priming of unfamiliar visual objects. Implications for theoretical models of object decision priming are discussed.

When a thought equals a look: refreshing enhances perceptual memory

Cognition constantly involves retrieving and maintaining information that is not perceptually available in the current environment. Studies on visual imagery and working memory suggest that such high-level cognition might, in part, be mediated by the revival of perceptual representations in the inferior temporal cortex. Here, we provide new support for this hypothesis, showing that reflectively accessed information can have similar consequences for subsequent perception as actual perceptual input. Participants were presented with pairs of frames in which a scene could appear, and were required to make a category judgment on the second frame. In the critical condition, a scene was presented in the first frame, but the second frame was blank. Thus, it was necessary to refresh the scene from the first frame in order to make the category judgment. Scenes were then repeated in subsequent trials to measure the effect of refreshing on functional magnetic resonance imaging repetition attenuation -- a neural index of memory -- in a scene-selective region of the visual cortex. Surprisingly, the refreshed scenes produced equal attenuation as scenes that had been presented twice during encoding, and more attenuation than scenes that had been presented once during encoding, but that were not refreshed. Thus, the top-down revival of a percept had a similar effect on memory as actually seeing the stimulus again. These findings indicate that high-level cognition can activate stimulus-specific representations in the ventral visual cortex, and that such top-down activation, like that from sensory stimulation, produces memorial changes that affect perceptual processing during a later encounter with the stimulus.

Are awareness questionnaires valid? Investigating the use of posttest questionnaires for assessing awareness in implicit memory tests

Two experiments--one employing a perceptual implicit memory test and the other a conceptual implicit memory test--investigated the validity of posttest questionnaires for determining the incidence of awareness in implicit memory tests. In both experiments, a condition in which none of the studied words could be used as test responses (i.e., the none-studied condition) was compared with a standard implicit test condition. Results showed that reports of awareness on the posttest questionnaire were much less frequent in the none-studied condition than in the standard condition. This was especially true after deep processing at study. In both experiments, 83% of the participants in the none-studied condition stated they were unaware even though there were strong demands for claiming awareness. Although there was a small bias in the questionnaire (i.e., 17% of the participants in the none-studied condition stated they were aware), overall, there was strong support for the validity of awareness questionnaires.

Equivalent inter- and intramodality long-term priming: Evidence for a common lexicon for words seen and words heard

Weaker inter- than intramodality long-term priming of words has promoted two hypotheses: (1) separate visual and auditory lexicons and (2) modality dependence of implicit memory. In five experiments, we employed manipulations aimed to minimize study-test asymmetries between the two priming conditions. Activities at visual and auditory study were matched, words were phonologically consistent, and study modality was manipulated between subjects. Equal magnitudes of inter- and intramodality priming were found in experiments with visual and auditory stem completion at test, with visual fragment completion at test, and with visual and auditory perceptual identification at test. A within-subjects experiment yielded the conventional intramodality advantage. The results point to a single amodal lexicon and to modality-independent phonological processing as the basis of implicit word memory.

What does it take to implicitly prime low-frequency category exemplars?

Prominent views of implicit priming agree that repetition of category exemplars should increase the probability of the exemplar coming to mind on a category production test. This prediction has been borne out in the data of numerous experiments that have used relatively high-frequency exemplars, but experiments that have used lower frequency exemplars have reported reduced or no priming on category production tests. Frameworks of memory disagree on why frequency would affect priming. The authors report 3 experiments, the first of which shows no priming of low-frequency exemplars under circumstances that yield priming of higher frequency instances. The second 2 experiments show that low-frequency instances can be primed, but the prior experience must bias the comprehension of the category label, not the exemplar.