Experienced and remembered pleasure for meals: duration neglect but minimal peak, end (recency) or primacy effects.

Rated liking for dishes consumed during a meal was compared with recalled liking in two studies using actual meals and one with an imagined meal. The effects on memory of the most pleasant dish, the first and last dishes, a rising vs. falling hedonic profile, and the time spent eating a dish were evaluated for similarity to effects seen in memories of pain. Across the three studies, there was consistent evidence for duration neglect (no effect of increased duration/exposure of the favorite component), and some weak evidence that patterns rising in liking are preferred to those falling in liking. In all three studies, there was no evidence for peak, primacy or recency effects. The existence of duration neglect implies that, with respect to memories of a meal, small portions of a highly favored dish will have roughly the same memorial effect as large portions.

Self-prediction of hedonic trajectories for repeated use of body products and foods: poor performance, not improved by a full generation of experience.

This study extends earlier work by [Kahneman, D., and Snell, J. (1992). Predicting a changing taste: Do people know what they will like? Journal of Behavioral Decision Making, 5, 187-200.]. suggesting that people are poor at predicting changes in liking. This is an important issue because an absence of this ability would make it difficult for people to optimize their own choices. Twenty undergraduates and 20 of their parents sampled four relatively unfamiliar consumer products, two foods and two body products, for 8 days. On Day 1, participants rated their initial liking and predicted their liking after seven daily uses of the products. Predictions were compared to actual liking on Day 8. Consistent with prior work, participants were poor at predicting their actual hedonic trajectories because they underestimated the degree to which their preferences would change. Contrary to predictions, parents were no better than students at this task, even though they had some 20-39 years more experience in observing their own hedonic trajectories. There is no evidence for any parent-child resemblance in either liking for the products or ability to accurately predict hedonic trajectory, and no evidence for consistency in ability to predict trajectories across the four different products. In general, participants underestimate the degree to which their preferences will change.

Flavour liking and preference conditioned by caffeine in humans.

When caffeine consumers repeatedly experience a novel flavoured drink containing caffeine, the rated pleasantness of the drink flavour increases progressively. These results could be interpreted in terms of the flavour acting as a Pavlovian conditioned stimulus (CS) predicting the consequences of caffeine ingestion. However, all studies of this phenomenon to date have used between-subjects designs, and one criticism of this is that changes in pleasantness might have arisen from nonspecific effects. A more rigorous test is to examine changes in pleasantness for two drinks, a CS+ flavour paired with caffeine and CS- paired with placebo. Accordingly, 20 moderate caffeine consumers consumed both CS+ and CS- drinks in counterbalanced order over eight conditioning trials at breakfast, with hedonic and sensory characteristics evaluated on each trial. As predicted, the rated pleasantness of the CS+ drink increased whereas pleasantness of the CS- drink did not change. Despite this, participants did not have an overall preference for the CS+ flavour posttraining. However, both those who chose the CS+ and those who chose the CS- at the end showed the same direction and rate of change in pleasantness for the two drinks during training, but spurious differences in baseline preference obscured this effect in terms of an overall change in preference. Overall these data suggest that changes in pleasantness of drinks paired with caffeine delivery are best explained in terms of Pavlovian, associations between drink flavour and the postingestive effects of caffeine.

How habitual caffeine consumption and dose influence flavour preference conditioning with caffeine.

This study investigated the effects of both habitual caffeine use and dose administered in determining the ability of caffeine to reinforce conditioned changes in flavour preference. Thirty overnight-withdrawn moderate caffeine consumers and 30 non or low-dose caffeine (non/low) consumers evaluated five novel-flavoured fruit teas. Subsequently, their median-rated tea was used in four ensuing conditioning sessions. Either placebo, 1 or 2 mg/kg of caffeine (n=10 consumers, 10 non/low consumers in each condition), was added to the target tea, and all five teas were reevaluated at a final tasting. Pleasantness ratings over the four conditioning sessions indicated that non/low consumers' liking increased for the noncaffeinated fruit tea with no change for the tea containing either 1 or 2 mg/kg of caffeine. Among consumers, pleasantness ratings tended to decrease for the noncaffeinated fruit tea but increased significantly at the 1-mg dose and showed a tendency to increase at the 2-mg dose. Similar effects were shown in the evaluations made before and after conditioning, with no change in the nonexposed drinks. These results show that 1.0 mg/kg of caffeine reinforces changes in flavour pleasantness in acutely withdrawn habitual consumers but not in nonconsumers or nondependent low-caffeine consumers, further endorsing the negative-reinforcement theory of conditioning with caffeine.

The influence of fat co-administration on the glucose memory facilitation effect.

Memory for a list of 20 words can be enhanced when learning is preceded by consumption of 25 g of glucose, compared with consumption of an equally sweet aspartame solution. The present study examined whether memory performance is also enhanced when glucose is administered in conjunction with another food constituent, in particular fat. Four groups of healthy young participants were tested under one of four conditions: (a) glucose + full-fat yoghurt; (b) glucose + fat-free yoghurt; (c) aspartame + full-fat yoghurt; (d) aspartame + fat-free yoghurt. The groups were compared on measures of blood glucose and cognitive performance. Participants receiving a glucose drink in conjunction with a fat-free yoghurt displayed higher blood glucose levels (BGL) and better performance on short- and long-delay recall of the word list compared with (a) individuals who consumed the glucose drink in conjunction with a full-fat yoghurt and (b) individuals who consumed the aspartame drink. The glycaemic data indicated that the presence of fat slows down glucose absorption. The findings suggest that only foods with a relatively fast glucose absorption rate are able to significantly enhance the encoding and long-term retention of novel memory materials in healthy young adults.

Impairments in working memory associated with naturalistic dieting in women: no relationship between task performance and urinary 5-HIAA levels.

The present study investigated the question of whether the previously observed impairments of working memory characteristic of dieting to lose weight can be explained in terms of preoccupying cognitions relating to body shape or to alterations in serotonergic function resulting from a low dietary intake of tryptophan. The population comprised female non-dieting, lower restrained eaters (N=23), non-dieting higher restrained eaters (N=11) and current dieters (N=19). Each participant completed three tasks, each of which selectively loaded on to a different sub-component of working memory. The tasks comprised the Tower of London task, a letter string recall task and a mental rotation task. In addition, all participants completed self-report measures of body shape concern and affective state. Serotonin turnover was assessed by means of 24 h urine sample collection for each participant on their day of testing. This was analysed (via HPLC) for levels of the main serotonin metabolite 5-HIAA.The results of the present study broadly replicated previous findings of a Central Executive and Phonological Loop (but not Visuo-Spatial Sketchpad) deficit in those subjects who reported themselves to be currently dieting. Tower of London task performance also significantly correlated with self-reported feelings of fatness and body shape disparagement. There were no group differences in 5-HIAA levels nor did 5-HIAA levels correlate with task performance. However, there was a significant negative correlation between 5-HIAA levels and self-reported depression. These results support the hypothesis that the variables mediating this deficit are preoccupying cognitions concerning body shape. They do not support the hypothesis that the serotonergic function of dieters is compromised, although this conclusion is tentative.

Caffeine reinforces flavour preference in caffeine-dependent, but not long-term withdrawn, caffeine consumers.

RATIONALE: Previous studies have shown that caffeine can reinforce flavour liking in overnight deprived moderate caffeine consumers (e.g. average of 250 mg/day) but not in low consumers (<120 mg/day). However, it is not possible to determine whether the difference between moderate and low caffeine consumers results from pre-existing individual differences in response to caffeine, or results directly from the different amounts of caffeine they habitually consume. If the former were true, then moderate consumers who are completely withdrawn should still manifest the flavour conditioning effect. Conversely, if the latter were true, consumers who are completely withdrawn should not manifest the effect. OBJECTIVES: To examine whether moderate caffeine consumers who have been fully withdrawn from caffeine manifest the flavour conditioning effect. METHODS: In a double-blind study, 48 moderate caffeine consumers refrained from consuming caffeine for 4 weeks and were given replacement drinks to consume, which were either caffeinated (maintained group) or decaffeinated (withdrawn group). In the final 2 weeks, all subjects evaluated a novel drink containing either 100 mg caffeine or placebo on four non-consecutive days. RESULTS. The rated pleasantness of the novel drink containing caffeine increased over the four test days in the group maintained on caffeine, but pleasantness of the same drink fell significantly in the withdrawn group. CONCLUSIONS: These data suggest that the ability of caffeine to reinforce changes in flavour liking are driven by the alleviation of withdrawal symptoms among habitual caffeine consumers and provide further support for the negative reinforcement theory.

Effect of color on expected and experienced refreshment, intensity, and liking of beverages.

The effect of color on the expected and experienced refreshment, intensity, and liking of lemon, mint, and vanilla beverages was studied. Subjects rated the expected and actual taste of brown lemon and mint solutions as less refreshing than the tastes of differently colored solutions of the same flavor. However, the refreshment ratings (expected and actual) of the brown vanilla beverage were not different from those of the vanilla beverages of other colors. Liking ratings also depended on color in a manner similar to that of the refreshment ratings. Intensity ratings also varied with color. However, unlike when subjects smell solutions rather than taste them, colored solutions were not judged as more intense than colorless ones. In fact, the clear solutions were judged as strongest.

The effect of retrograde and anterograde glucose administration on memory performance in healthy young adults.

Memory for a list of 20 words can be enhanced by preceding learning by consumption of 25 g of glucose, compared with consumption of an equally sweet aspartame solution (Psychopharmacology 137 (1998) 259; Psychopharmacology 157 (2001) 46). However, using this anterograde administration procedure, it is impossible to separate whether glucose affects encoding, consolidation, or retrieval. The present placebo-controlled, double-blind study investigated the effect of anterograde and retrograde administration on memory performance in healthy young participants. In order to evaluate whether post-acquisition administration of glucose can improve memory performance and to compare possible differences in the size of the effect, participants were administered 25 g of glucose immediately before or immediately after presentation of a word list. Moreover, in order to investigate whether the effect of glucose administration on memory performance is time-dependent, a third group received 25 g of glucose 15 min before learning the word list. Word- list recall was tested 30 min and 24 h after word list presentation. Measures of spatial memory performance and working memory were also evaluated. The results of this study showed that both pre- and post-acquisition oral glucose administration (25 g) can improve memory performance. However, as the time interval between anterograde glucose administration and memory encoding increased, the glucose memory facilitation effect decreased. This study provides evidence that glucose enhances memory performance in healthy young people even when it is given after learning has taken place, and that this effect is observed at least up to 24 h after glucose administration. Moreover, it provides evidence that the effect of glucose on memory performance may be time-dependent, as the enhancement of retention was decreased when the administration-learning interval was increased.

Effect of caffeine-deprivation on liking for a non-caffeinated drink.

Liking for a novel non-caffeinated drink decreases when regular caffeine consumers are exposed repeatedly to that drink when caffeine-deprived; however, this dislike is not manifest if people are subsequently tested when not caffeine-deprived (Yeomans et al., 2000a). The present study investigated the basis for this effect, and in particular, whether the decrease in liking observed is specific to the drink flavour experienced during caffeine-deprivation. Twenty-four caffeine consumers evaluated five novel drinks (fruit teas) at pre-training. For each person, the drink with the median liking score was subsequently consumed mid-morning after 12 h caffeine-deprivation on four non-consecutive training days. Rated pleasantness of this drink decreased significantly over these four training days. Subjects subsequently re-evaluated all five drinks on a test day when half the consumers were given 100mg caffeine two hours prior to testing, with the remainder receiving placebo. The group who remained deprived continued to express depressed liking for the exposed (target) drink, compared to their pre-training rating of that drink. In contrast, rated pleasantness was not depressed compared to pre-training ratings in the group who had received caffeine prior to testing. Rated pleasantness of the four unexposed drinks was equivalent to pre-training ratings, for both groups, suggesting that the effect of exposure on ratings of the target drink was specific to that drink. As expected, there was some evidence of improved mood in the group receiving caffeine on the test day; but as it was only ratings of the target drink that differed across groups, the group difference cannot be attributed to general effects of mood on use of the rating scale. These data suggest that the reversal of acquired changes in liking for drinks when consumers are changed from a caffeine-deprived to an undeprived condition is best explained in terms of state-dependent learning, that is specific to the drink experienced during caffeine-deprivation.

Investigation into the significance of task difficulty and divided allocation of resources on the glucose memory facilitation effect.

RATIONALE: Memory for a list of 20 words can be enhanced by preceding learning with consumption of 25 g glucose rather than an equally sweet aspartame solution. In previous studies, participants performed a secondary hand-movement task during the list-learning phase. OBJECTIVE: The present placebo-controlled, double-blind study examined whether the additional cognitive load created by a secondary task is a crucial feature of the glucose memory facilitation effect. METHODS: The effect of glucose administration on word recall performance in healthy young participants was examined under conditions where the primary memory task and a secondary task were competing for cognitive resources (across a range of secondary tasks), and where task difficulty was increased but dual task-mediated competition for cognitive resources did not exist. Measures of non-verbal and working memory performance were also compared under the different glycaemic conditions (glucose versus aspartame drinks). RESULTS: In the present study, a beneficial effect of glucose on memory was detected after participants encoded a 20-word list while performing a secondary task, but not when participants encoded the list without a secondary task, nor when the 20 target words were intermixed with 20 non-target words (distinguished by gender of speaker). In addition, glucose significantly enhanced performance on spatial and working memory tasks. CONCLUSION: The data indicate that possible "depletion" of episodic memory capacity and/or glucose-mediated resources in the brain due to performing a concomitant cognitive task might be crucial to the demonstration of a glucose facilitation effect. Possible implications regarding underlying cognitive and physiological mechanisms are discussed in this article.