Chimpanzee (Pan troglodytes) intentional communication is not contingent upon food

Studies of great apes have revealed that they use manual gestures and other signals to communicate about distal objects. There is also evidence that chimpanzees modify the types of communicative signals they use depending on the attentional state of a human communicative partner. The majority of previous studies have involved chimpanzees requesting food items from a human experimenter. Here, these same communicative behaviors are reported in chimpanzees requesting a tool from a human observer. In this study, captive chimpanzees were found to gesture, vocalize, and display more often when the experimenter had a tool than when she did not. It was also found that chimpanzees responded differentially based on the attentional state of a human experimenter, and when given the wrong tool persisted in their communicative efforts. Implications for the referential and intentional nature of chimpanzee communicative signaling are discussed.     

On the contribution of perceptual fluency and priming to recognition memory

Repetition priming has been shown to be independent of recognition memory. Thus, the severely amnesic patient E.P. has demonstrated intact stem completion priming and perceptual identification priming, despite at-chance performance on recognition memory tasks. It has also been shown that perceptual fluency can influence feelings of familiarity, in the sense that items perceived more quickly tend to be identified as familiar. If studied items are identified more fluently, due to perceptual priming, and fluency leads to familiarity, why do severely amnesic patients perform no better than chance on recognition memory tasks? One possibility is that severely amnesic patients do not exhibit normal fluency. Another possibility is that fluency is not a sufficiently strong cue for familiarity. In two experiments, 2 severely amnesic patients, 3 moderately amnesic patients, and 8 controls saw words slowly clearing from a mask. The participants identified each word as quickly as possible and then made a recognition (old/new) judgment. All the participants exhibited fluency, in that old responses were associated with shorter identification times than new responses were. In addition, for the severely amnesic patients, priming was intact, and recognition memory performance was at chance. We next calculated how much priming and fluency should elevate the probability of accurate recognition. The tendency to identify studied words rapidly (.6) and the tendency to label these rapidly identified words old (.6) would result in 36% of the studied words being labeled old. Other studied words were identified slowly (.4) but were still labeled old (.4), resulting in an additional 16% of studied words labeled old. Thus, the presence of fluency increases the probability of accurate recognition judgments to only 52% (chance = 50%). This finding explains why amnesic patients can exhibit both priming and fluency yet still perform at chance on recognition tests.     

Impaired odor recognition memory in patients with hippocampal lesions

In humans, impaired recognition memory following lesions thought to be limited to the hippocampal region has been demonstrated for a wide variety of tasks. However, the importance of the human hippocampus for olfactory recognition memory has scarcely been explored. We evaluated the ability of memory-impaired patients with damage thought to be limited to the hippocampal region to recognize a list of odors. The patients were significantly impaired after a retention delay of 1 h. Olfactory sensitivity was intact. This finding is in agreement with earlier reports that rats with hippocampal lesions exhibited memory impairment on an odor delayed nonmatching to sample task (after 30 min and 1 h) and that patients with damage thought to be limited to the hippocampal region were impaired on an odor span memory task. Olfactory recognition memory, similar to recognition memory in other sensory modalities, depends on the integrity of the hippocampal region.     

Associative change in the representations acquired during conditional discriminations: further analysis of the nature of conditional learning

Three experiments with rats investigated how the associative strengths of the representations that underlie conditional learning change when they are conditioned in compound. The results of each experiment suggest that the representation whose associative strength is most discrepant from the asymptote supported by the outcome of the trial undergoes the greatest change in associative strength. These results parallel those from simple Pavlovian conditioning (e.g., R. A. Rescorla, 2000). are inconsistent with unique-cue and configural accounts of conditional learning, and support a connectionist analysis of learning in which a "winner-takes-all" rule applies to the hidden units that can be activated and acquire associative strength at a given point in time.     

Braking reaching movements: a test of the constant tau-dot strategy under different viewing conditions

Following F. Zaal and R. J. Bootsma (1995), the authors studied whether the decelerative phase of a reaching movement could be modeled as a constant tau-dot strategy resulting in a soft collision with the object. Specifically, they investigated whether that strategy is sustained over different viewing conditions. Participants (N = 11) were required to reach for 15- and 50-mm objects at 2 different distances under 3 conditions in which visual availability of the immediate environment and of the reaching hand were varied. Tau-dot estimates and goodness-of-fit were highly similar across the 3 conditions. Only within-participant variability of tau-dot estimates was increased when environmental cues were removed. That finding suggests that the motor system uses a tau-dot strategy involving the intermodal (i.e., visual, proprioceptive, or both) specification of information to regulate the decelerative phase of reaching under restricted viewing conditions. The authors provide recommendations for improving the derivation of tau;(x) estimates and stress the need for further research on how time-to-contact information is used in the regulation of the dynamics of actions such as reaching.     

Active-imaginal exposure: examination of a new behavioral treatment for cynophobia (dog phobia)

The aims of this study were to investigate exposure-based treatments for cynophobia (dog phobia) and to test a newly developed hybrid imaginal exposure treatment that we have named active imaginal exposure. The treatment introduces an in vivo coping component to imaginal exposure whereby the patient physically performs coping responses to an imagined feared stimulus. Eighty-two participants meeting DSM-IV criteria for specific phobia (animal subtype) were randomly assigned to one of three 30-min. treatments: (a) active-imaginal exposure (AI), (b) imaginal exposure alone (IE), or (c) graduated in vivo exposure (IV). Participants completed a behavioral approach test at pre, post, and four-week follow-up. Significant pre- to posttreatment improvement was observed in all three treatment conditions. Response rates at posttreatment were 51.9, 62.1, and 73.1% for the IE, AI, and IV groups respectively. Likewise, effect sizes at posttreatment were 0.76, 1.41, and 1.55 for the IE, AI, and IV groups respectively. Although in the predicted direction, the between group differences were not significant. A similar pattern of results was observed at follow-up. Further, safety behavior utilization during treatment was associated with less improvement--particularly in the two imaginal treatment conditions. Exposure treatments of dog phobia appear feasible and effective in reducing phobic fear and avoidance associated with dog phobia. Furthermore, preliminary evidence suggests that our active-imaginal exposure treatment may be a viable alternative to in vivo exposure.     

The use of bouts and frequencies in the evaluation of hand preferences for a coordinated bimanual task in chimpanzees (Pan troglodytes): an empirical study comparing two different indices of laterality

Hand preferences for a coordinated bimanual task were assessed in 109 chimpanzees (Pan troglodytes). Hand preference was evaluated for 4 test sessions using bouts and frequencies of hand use to compare the sensitivity of each level of analysis in evaluating individual variation in handedness. Overall, significant population-level right-handedness was found using several different measures of hand use. Handedness indices based on bouts and frequencies were highly and significantly correlated. Moreover, hand preferences were consistent across tests despite efforts to situationally bias preference during each test. Taken together, these data do not support the view that bouts are a better level of analysis for evaluating hand preference. The results further suggest that hand preferences for coordinated bimanual actions are not influenced by situational factors and may reflect an inherent specialization of the left hemisphere for motor skill.     

The whole-hand point: the structure and function of pointing from a comparative perspective

Pointing by monkeys, apes, and human infants is reviewed and compared. Pointing with the index finger is a species-typical human gesture, although human infants exhibit more whole-hand pointing than is commonly appreciated. Captive monkeys and feral apes have been reported to only rarely "spontaneously" point, although apes in captivity frequently acquire pointing, both with the index finger and with the whole hand, without explicit training. Captive apes exhibit relatively more gaze alternation while pointing than do human infants about 1 year old. Human infants are relatively more vocal while pointing than are captive apes, consistent with paralinguistic use of pointing.