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.     

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.     

The influence of learning methods on collaboration: prior repeated retrieval enhances retrieval organization, abolishes collaborative inhibition, and promotes post-collaborative memory

Research on collaborative memory has unveiled the counterintuitive yet robust phenomenon that collaboration impairs group recall. A candidate explanation for this collaborative inhibition effect is the disruption of people's idiosyncratic retrieval strategies during collaboration, and it is hypothesized that employing methods that improve one's organization protects against retrieval disruption. Here it is investigated how one's learning method during the study phase--defined as either repeatedly studying or repeatedly retrieving information--influences retrieval organization and what effects this has on collaborative recall and post-collaborative individual recall. Results show that repeated retrieval consistently eliminated collaborative inhibition. This enabled participants to gain the most from re-exposure to materials recalled by their partners that they themselves did not recall and led to improvements in their individual memory following collaboration. This repeated retrieval advantage stemmed from the preferential manner in which this learning method strengthened retrieval organization. Findings are also discussed that reveal a relationship between retrieval organization and the interaction observed between learning method and short versus long delay seen in the testing effect literature. Finally, results show that the elusive benefits of cross-cuing during collaboration may be best detected with a longer study-test delay. Together, these findings illuminate when and how collaboration can enhance memory.     

Study repetition and divided attention: Effects of encoding manipulations on collaborative inhibition in group recall

Two experiments tested the effects of encoding manipulations on group recall and on the magnitude of collaborative inhibition. Collaborative inhibition refers to the phenomenon where by a collaborative group recalls less than do the same number of individuals who work alone and then have their nonredundant responses pooled. Participants studied categorized word lists once or three times (Experiment 1) or under conditions of full versus divided attention (Experiment 2). Study repetition both improved retrieval organization in recall and attenuated collaborative inhibition, and divided attention encoding both reduced retrieval organization in recall and eliminated collaborative inhibition. These experiments are the first to focus on encoding variables and to show that collaborative inhibition can vary as a function of encoding manipulations.     

Collaborative memory and part-set cueing impairments: the role of executive depletion in modulating retrieval disruption

When people are exposed to a subset of previously studied list items they recall fewer of the remaining items compared to a condition where none of the studied items is provided during recall. This occurs both when the subset of items is provided by the experimenter (i.e., the part-set cueing deficit in individual recall) and when they are provided during the course of a collaborative discussion (i.e., the collaborative inhibition effect in group recall). Previous research has identified retrieval disruption as a common mechanism underlying both effects; however, less is known about the factors that may make individuals susceptible to such retrieval disruption. In the current studies we tested one candidate factor: executive control. Using an executive depletion paradigm we directly manipulated an individual's level of executive control during retrieval. Results revealed no direct role of executive depletion in modulating retrieval disruption. In contrast, executive control abilities were indirectly related to retrieval disruption through their influence at encoding. Together these results suggest that executive control des not directly affect retrieval disruption at the retrieval stage, and that the role of this putative mechanism may be limited to the encoding stage.     

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.     

Fact learning: how information accuracy, delay, and repeated testing change retention and retrieval experience

Previous classroom studies have shown that the phenomenology of studied facts changes over time. However, pedagogical needs preclude both the study of errors and the separation of the effects that delay and repeated testing have on retention and retrieval experience. We addressed these issues together in an experiment where participants read stories containing correct and misleading information and provided Remember, Just Know, and Familiar judgements on immediate and delayed general knowledge tests. After 2 days, information learned from the stories shifted from Remembered to Just Known, but repeated testing attenuated this shift. Interestingly, similar patterns of retrieval and phenomenology were observed for correct and misleading information with one important difference--the shift over time to Just Knowing was significantly greater for correct than for misleading information. Together, these findings show the roles of information accuracy, delay, and testing in determining both retention and the subjective experience of retrieval.     

Adolescent development of motor imagery in a visually guided pointing task

The development of action representation during adolescence was investigated using a visually guided pointing motor task (VGPT) to test motor imagery. Forty adolescents (24 males; mean age 13.1 years) and 33 adults (15 males; mean age 27.5 years) were instructed to both execute and imagine hand movements from a starting point to a target of varying size. Reaction time (RT) was measured for both Execution (E) and Imagery (I) conditions. There is typically a close association between time taken to execute and image actions in adults because action execution and action simulation rely on overlapping neural circuitry. Further, representations of actions are governed by the same speed-accuracy trade-off as real actions, as expressed by Fitts’ Law. In the current study, performance on the VGPT in both adolescents and adults conformed to Fitts’ Law in E and I conditions. However, the strength of association between E and I significantly increased with age, reflecting a refinement in action representation between adolescence and adulthood.     

Context learning for threat detection

It is hypothesised that threatening stimuli are detected better due to their salience or physical properties. However, these stimuli are typically embedded in a rich context, motivating the question whether threat detection is facilitated via learning of contexts in which threat stimuli appear. To address this question, we presented threatening face targets in new or old spatial configurations consisting of schematic faces and found that detection of threatening targets was faster in old configurations. This indicates that individuals are able to learn regularities within visual contexts and use this contextual information to guide detection of threatening targets. Next, we presented threatening and non-threatening face targets embedded in new or old spatial configurations. Detection of threatening targets was facilitated in old configurations, and this effect was reversed for non-threatening targets. Present findings show that detection of threatening targets is driven not only by stimulus properties as theorised traditionally but also by learning of contexts in which threatening stimuli appear. Further, results show that context learning for threatening targets obstructs context learning for non-threatening targets. Overall, in addition to typically emphasised bottom-up factors, our findings highlight the importance of top-down factors such as context and learning in detection of salient, threatening stimuli.