Stephen A. Dewhurst

Emotionality, distinctiveness, and recollective experience

Two experiments investigated the effects of emotional stimuli on recollective experience in recognition memory. In Experiment 1, words judged to evoke a positive emotional response (e.g., warmth, freedom) or a negative emotional response (e.g., mucus, corpse) were associated with more “remember” responses than emotionally neutral words (e.g., crate, border) when presented in mixed lists. This effect was stronger with negative words than with positive words. In Experiment 2 the effects of emotional stimuli were eliminated when participants studied pure lists of either all emotional or all neutral words. These findings are discussed in relation to Rajarams (1996) distinctiveness account of recollective experience.

Effects of exact and category repetition in true and false recognition memory

Two experiments used the distinction between remembering and knowing to investigate the effects of exact and category repetition in recognition memory. In Experiment 1, exact repetition enhanced remember responses but had no reliable effect onknow responses. In Experiment 2, category repetition enhanced correct know responses but had no effect on correct remember responses. Category repetition also increased false positive remember and know responses. It is argued that exact repetition influences the recollection component of recognition memory via the creation of multiple episodic traces, each of which is potentially capable of supporting a remember response, whereas category repetition influences the familiarity component of recognition memory by enhancing the fluency with which test items are processed.

Measuring the speed of the conscious components of recognition memory: remembering is faster than knowing

Three experiments investigated response times (RTs) for remember and know responses in recognition memory. RTs to remember responses were faster than RTs to know responses, regardless of whether the remember-know decision was preceded by an old/new decision (two-step procedure) or was made without a preceding old/new decision (one-step procedure). The finding of faster RTs for R responses was also found when remember-know decisions were made retrospectively. These findings are inconsistent with dual-process models of recognition memory, which predict that recollection is slower and more effortful than familiarity. Word frequency did not influence RTs, but remember responses were faster for words than for nonwords. We argue that the difference in RTs to remember and know responses reflects the time taken to make old/new decisions on the basis of the type of information activated at test.

Collaborative false recall in the DRM procedure: Effects of group size and group pressure

Basden, Basden, Thomas, and Souphasith (1998) demonstrated that false recall in collaborative trios is enhanced when group members feel under pressure to output items. In the present study, individuals, pairs, trios, and quartets were presented with lists of words drawn from the Deese-Roediger-McDermott paradigm. Memory was tested under high or low group pressure conditions. It was found that false recall increased in proportion to group size regardless of group pressure, but that groups experiencing the most pressure to output items made a greater number of errors. Furthermore, on a surprise later individual recall test, participants who experienced the most pressure during collaboration retained an equivalent level of critical lures. Collectively these findings demonstrate that group pressure can increase collaborative false recall, and that these false memories can be retained beyond group testing.

Remembering the past and imagining the future: differences in event specificity of spontaneously generated thought.

A growing interest has emerged in the role that autobiographical memory retrieval plays in simulation of future events. Cognitive explorations in this domain have generally relied on cue word paradigms with instructions to develop specific (relating to one particular day) memories or future events. However, the usefulness of this paradigm has been questioned with respect to its ability to assess habitual patterns of retrieval within autobiographical memory. The current study investigated similarities and differences in how participants spontaneously remember the past and imagine the future when the specificity constraints inherent in the cue word task are removed. A total of 93 undergraduate students completed two sentence-completion tasks, probing for past and future events. A number of differences emerged between past and future thought; in particular, they were less specific when simulating future events compared with past events. This reduction in specificity was the result of participants producing more future thoughts relating to extended lifetime periods and semantic associates. The findings are discussed in relation to the underlying cognitive processes involved in autobiographical memory retrieval and future event simulation.

Cognitive Effort and Recollective Experience in Recognition Memory

The difficulty of the cognitive operations required to process study items was manipulated in two experiments investigating recollective experience. In subsequent recognition tests, subjects indicated whether their recognition judgements for items processed in these tasks were based on recollection (remember responses) or on familiarity (know responses). In Experiment 1 target items were presented in the context of a category decision task. It was found that remember responses increased with the difficulty of the category decision. For positive instances, remember responses were greater for items of low instance frequency than for items of high instance frequency, while for negative instances remember responses were greater for items from similar categories than for items from dissimilar categories. These effects were not present in know responses. In Experiment 2, remember responses were more frequent when study items had been presented in the form of anagrams to be solved than when they had been presented in the form of words to be read aloud. The incidence of know responses was not affected by the format in which study items were presented. Source judgements were also more accurate when recognition was based on recollection. It is argued that the type of conscious awareness experienced during recognition is determined by the knowledge activated by items presented in the recognition test, which in turn is determined by the nature of the operations engaged at encoding.

Selective interference with the use of visual images in the symbolic distance paradigm.

Eight experiments investigated the effects of visual, spatial, auditory, and executive interference on the symbolic comparison of animal size and ferocity, semantic goodness of words, and numbers. Dynamic visual noise (DVN) and the reading of visually presented stimulus items were shown to selectively interfere with response times on the animal size comparison task, though the slope of the symbolic distance function remained unchanged. Increased change of DVN significantly increased interference, but interference was reduced by equiluminant DVN. Spatial tracking reduced the slope of the symbolic distance function in contrast to an executive task that only increased mean latency and errors for all comparisons. Results suggest that the generation of an image is necessary for size comparison, but neither imagery nor executive function is responsible for the frequently observed distance-time function.

Dynamic Visual Noise Interferes with Storage in Visual Working Memory

Several studies have demonstrated that dynamic visual noise (DVN) does not interfere with memory for random matrices. This has led to suggestions that (a) visual working memory is distinct from imagery, and (b) visual working memory is not a gateway between sensory input and long-term storage. A comparison of the interference effects of DVN with memory for matrices and colored textures shows that DVN can interfere with visual working memory, probably at a level of visual detail not easily supported by long-term memory structures or the recoding of the visual pattern elements. The results support a gateway model of visuospatial working memory and raise questions about the most appropriate ways to measure and model the different levels of representation of information that can be held in visual working memory.

Shared cognitive processes underlying past and future thinking:the impact of imagery and concurrent task demands on event specificity

Recent literature has argued that whereas remembering the past and imagining the future make use of shared cognitive substrates, simulating future events places heavier demands on executive resources. These propositions were explored in 3 experiments comparing the impact of imagery and concurrent task demands on speed and accuracy of past event retrieval and future event simulation. Results provide support for the suggestion that both past and future episodes can be constructed through 2 mechanisms: a noneffortful direct pathway and a controlled, effortful generative pathway. However, limited evidence emerged for the suggestion that simulating of future, compared with retrieving past, episodes places heavier demands on executive resources; only under certain conditions did it emerge as a more error prone and lengthier process. The findings are discussed in terms of how retrieval and simulation make use of the same cognitive substrates in subtly different ways.

The effect of divided attention on false memory depends on how memory is tested.

In three experiments, we investigated the effects of divided attention on false memory, using the Deese/ Roediger-McDermott (DRM) paradigm. In Experiments 1 and 2, participants studied six DRM lists with full attention and six in one of two divided-attention conditions (random number generation or digit monitoring). Both divided-attention conditions increased false recall of related words (Experiment 1) but reduced false recognition (Experiment 2). These results were confirmed in Experiment 3, in which the type of secondary task was manipulated within groups. We argue that the increase in false recall with divided attention reflects a change in participants’ response criterion, whereas the decrease in false recognition occurs because the secondary tasks prevent participants from generating associates of the words presented at study.