Suparna Rajaram

Remembering and knowing : two means of access to the personal past

The nature of recollective experience was examined in a recognition memory task. Subjects gave “remember” judgments to recognized items that were accompanied by conscious recollection and “know” judgments to items that were recognized on some other basis. Although a levels-of-processing effect (Experiment 1) and a picture-superiority effect (Experiment 2) were obtained for overall recognition, these effects occurred only for “remember” judgments, and were reversed for “know” judgments. In Experiment 3, targets and lures were either preceded by a masked repetition of their own presentation (thought to increase perceptual fluency) or of an unrelated word. The effect of perceptual fluency was obtained for overall recogrntion and “know” judgments but not for “remember” judgments. The data obtained for confidencejudgments using the same design (Experiment4) indicated that “remember”/”know” judgments are not made solely on the basis of confidence. These data support the two-factor theories of recognition memory by dissociating two forms of recognition, and shed light on the nature of conscious recollection.

Direct comparison of four implicit memory tests.

Four verbal implicit memory tests, word identification, word stem completion, word fragment completion, and anagram solution, were directly compared in one experiment and were contrasted with free recall. On all implicit tests, priming was greatest from prior visual presentation of words, less (but significant) from auditory presentation, and least from pictorial presentations. Typefont did not affect priming. In free recall, pictures were recalled better than words. The four implicit tests all largely index perceptual (lexical) operations in recognizing words, or visual word form representations.

Perceptual effects on remembering: Recollective processes in picture recognition memory.

In 3 experiments, the effects of perceptual manipulations on recollective experience were tested. In Experiment 1, a picture-superiority effect was obtained for overall recognition and Remember judgements in a picture recognition task. In Experiment 2, size changes of pictorial stimuli across study and test reduced recognition memory and Remember judgements. In Experiment 3, deleterious effects of changes in left-right orientation of pictorial stimuli across study and test were obtained for Remember judgements. An alternate framework that emphasizes a distinctiveness-fluency processing distinction is proposed to account for these findings because they cannot easily be accommodated within the existing account of differences in conceptual and perceptual processing for the 2 categories of recollective experience: Remembering and Knowing, respectively (J. M. Gardiner, 1988; S. Rajaram, 1993).

Role of the anterior cingulate and medial orbitofrontal cortex in processing drug cues in cocaine addiction

Our goal in the current report was to design a new functional magnetic resonance imaging (fMRI) task to probe the role of the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) in processing of salient symptom-related cues during the simultaneous performance of an unrelated task in drug-addicted persons. We used a novel fMRI color-word drug Stroop task in 14 individuals with cocaine use disorders; subjects had to press for color of drug vs. matched neutral words. Although there were no accuracy or speed differences between the drug and neutral conditions in the current sample of subjects, drug words were more negatively valenced than the matched neutral words. Further, consistent with prior reports in individuals with other psychopathologies using different Stroop fMRI paradigms, our more classical color-word Stroop design revealed bilateral activations in the caudal-dorsal anterior cingulate cortex (cdACC) and hypoactivations in the rostro-ventral anterior cingulate cortex/medial orbitofrontal cortex (rACC/mOFC). A trend for larger rACC/mOFC hypoactivations to the drug than neutral words did not survive whole-brain corrections. Nevertheless, correlation analyses indicated that (1) the more the cdACC drug-related activation, the more negative the valence attributed to the drug words (r=-0.86, P<0.0001) but not neutral words; and (2) the more the rACC/mOFC hypoactivation to drug minus neutral words, the more the errors committed specifically to the drug minus neutral words (r=0.85, P<0.0001). Taken together, results suggest that this newly developed drug Stroop fMRI task may be a sensitive biobehavioral assay of the functions recruited for the regulation of responses to salient symptom-related stimuli in drug-addicted individuals.

What Causes Humans to Begin and End a Meal? A Role for Memory for What Has Been Eaten, as Evidenced by a Study of Multiple Meal Eating in Amnesic Patients

Although many factors have been proposed and studied as causes of onset and termination of meals by humans, little attention has been paid to memory for what has previously been eaten. We propose that a principal determinant of meal onset and cessation in humans is memory of when a last meal was eaten and how much was consumed. Knowledge that one has just eaten a culturally defined complete meal may be sufficient grounds for refusal of further food. This hypothesis was tested by studying two densely amnesic patients who had almost no explicit memory for events that occurred more than a minute ago, and who, in particular, usually failed to remember that they had just eaten a meal. Both patients (on three occasions each) readily consumed a second lunch when it was offered 10 to 30 min after completion of the first meal, and usually began to consume a third meal when it was offered 10 to 30 min after completion of the second meal. These findings suggest that memory for what has recently been eaten is a substantial contributor to the onset or cessation of eating of a meal.

Addiction changes orbitofrontal gyrus function: involvement in response inhibition.

We used the Stroop task as a measure of the ability to inhibit a prepotent response tendency and examined its association with relative glucose metabolism in selected prefrontal brain regions in cocaine addicts, alcoholics, and controls (17 per group). Results revealed that for the substance abusers, higher orbitofrontal gyrus (OFG) activation was associated with lower conflict (higher score;r = 0.32, p < 0.05). For the controls, higher OFG activation was associated with higher conflict (lower score;r = −0.42, p < 0.05). Thus, at baseline, increased relative activation of the OFG is associated with worse performance in controls and better performance in substance abusers on the Stroop task, suggesting reversal of the role of the OFG as a function of addiction.

Collaborative Memory: Cognitive Research and Theory:

People often form and retrieve memories in the company of others. Yet, nearly 125 years of cognitive research on learning and memory has mainly focused on individuals working in isolation. Although important topics such as eyewitness memory and autobiographical memory have evaluated social influences, a study of group memory has progressed mainly within the provinces of history, anthropology, sociology, and social psychology. In this context, the recent surge in research on the cognitive basis of collaborative memory marks an important conceptual departure. As a first aim, we review these empirical and theoretical advances on the nature and influence of collaborative memory. Effects of collaboration are counterintuitive because individuals remember less when recalling in groups. Collaboration can also lead to forgetting and increase memory errors. Conversely, collaboration can also improve memory under proper conditions. As a second aim, we propose an overarching theoretical framework that specifies the cognitive mechanisms associated with the costs and benefits of collaboration on memory. A study of the reciprocal influences of the group and the individual on memory processes naturally draws upon several disciplines. Our aim is to elucidate the cognitive components of this complex phenomenon and situate this analysis within a broader interdisciplinary perspective.

Conceptual fluency selectively influences knowing

Research shows that Remember and Know judgments are effective measures of recollective experience. This article shows that Know responses can be selectively affected by fluency of processing that is created using a conceptual manipulation. In a recognition test, studied and nonstudied words were preceded by semantically related or unrelated primes. Participants gave significantly more Know judgments to items with related primes than unrelated primes but Remember responses were unaffected. Know responses are discussed in terms of familiarity assumed to arise from fluency of processing which, in turn, may be created through various sources including conceptual processes.

The effects of conceptual salience and perceptual distinctiveness on conscious recollection

Two experiments were conducted to examine the hypothesis that recollective experience is influenced by the manipulation of salient or distinctive dimensions of the encoded stimuli (Rajaram, 1996). In Experiment 1, the conceptual dimension of the to-be-remembered homographs (bank) was manipulated by requiring subjects to encode the dominant (money-BANK) or the nondominant (river-BANK) meanings. In Experiment 2, the perceptual dimension was manipulated by presenting orthographically distinctive (subpoena) or orthographically common (sailboat) words. An advantage for conceptually salient (dominant meaning) items and perceptually distinctive (orthographically distinctive) items was selectively observed inremember responses. These results support the hypothesis that processing of distinctive or salient attributes boosts the recollective component of explicit memory.

Influence of re-exposure and retrieval disruption during group collaboration on later individual recall

This research examined the influence of prior group collaboration on later individual recall. We considered the negative effects of retrieval disruption and the potentially positive effects of re-exposure to additional items during group recall in the context of three hypotheses: the individual-strategy hypothesis, the combined-strategy hypothesis, and the group-strategy hypothesis. After a study phase and a brief delay, participants completed three successive recall trials in four different recall sequence conditions: III (individual-individual-individual), ICI (individual-collaborative-individual), CII (collaborative-individual-individual), and CCI (collaborative-collaborative-individual). Results show that repeated group recalls (CCI), and securing individual retrieval organisation prior to group recall (ICI), benefit later individual recall more than repeated individual recalls (III). These findings support the group-strategy hypothesis and the individual-strategy hypothesis, and have important implications for group versus individual learning practices in educational settings.