Criteria of reproductive success

To determine reproductive success, it is necessary for the researcher to specify a criterion of success, such as the number of a parent's offspring living to the age of reproduction. A measurement model, which includes the researcher's choice of criterion, has been proposed to estimate the lifetime reproductive success (R) of long-lived animals from complete or incomplete knowledge of the reproductive life histories of mothers and the survival fates of offspring. This research uses R and data from female baboons of Mikumi National Park, Tanzania, as vehicles to investigate the relationship between reproductive success and several criteria. Secondarily, it also investigates the relationship between R and the number and rate of offspring production. Seven criteria of reproductive success, ranging in 12-month increments from 0 (birth) to 72 months of offspring life, were applied to 10.5 years of reproductive data from 61 Mikumi females. Theoretically, the best scenario for comparative purposes is an invariant R across different criteria; however, the mean R systematically increased as the criteria increased. This is more an inconvenience than a serious problem because high correlations indicate high predictability between Rs from pairs of criteria. R was modestly correlated with the rate of offspring production, indicating that rate can be employed as a rough index of reproductive success. The choice of a criterion is a trade off between theory, practicality, the strength of the criterion, and the effect of the choice upon sample representativeness and size. Am. J. Primatol. 41:87–101, 1997. © 1997 Wiley-Liss, Inc.     

Different Levels of Food Restriction Reveal Genotype-Specific Differences in Learning a Visual Discrimination Task

In behavioural experiments, motivation to learn can be achieved using food rewards as positive reinforcement in food-restricted animals. Previous studies reduce animal weights to 80–90% of free-feeding body weight as the criterion for food restriction. However, effects of different degrees of food restriction on task performance have not been assessed. We compared learning task performance in mice food-restricted to 80 or 90% body weight (BW). We used adult wildtype (WT; C57Bl/6j) and knockout (ephrin-A2^−/−) mice, previously shown to have a reverse learning deficit. Mice were trained in a two-choice visual discrimination task with food reward as positive reinforcement. When mice reached criterion for one visual stimulus (80% correct in three consecutive 10 trial sets) they began the reverse learning phase, where the rewarded stimulus was switched to the previously incorrect stimulus. For the initial learning and reverse phase of the task, mice at 90%BW took almost twice as many trials to reach criterion as mice at 80%BW. Furthermore, WT 80 and 90%BW groups significantly differed in percentage correct responses and learning strategy in the reverse learning phase, whereas no differences between weight restriction groups were observed in ephrin-A2^−/− mice. Most importantly, genotype-specific differences in reverse learning strategy were only detected in the 80%BW groups. Our results indicate that increased food restriction not only results in better performance and a shorter training period, but may also be necessary for revealing behavioural differences between experimental groups. This has important ethical and animal welfare implications when deciding extent of diet restriction in behavioural studies.     

Exploration of a novel space is associated with individual differences in learning speed in black-capped chickadees, Poecile atricapillus

Individual variation in exploratory behaviour has been demonstrated in a diverse array of animal species. Understanding the evolutionary antecedents and ecological consequences of this variation is an active research area within animal behaviour. Here we investigate whether different exploration styles exhibited by black-capped chickadees (Poecile atricapillus) in a novel environment are related to how quickly these birds learn an acoustic discrimination task. We found that birds that readily enter a novel environment learn an acoustic discrimination task faster than birds that do not readily enter a novel environment. This result contrasts with previous work suggesting no correlation between exploration style and learning a spatial or associative task in great tits (Parus major), a close relative of the black-capped chickadee.     

Rhesus monkey (Macaca mulatta) complex learning skills reassessed

Results from three experiments on basic learning and transfer in rhesus monkeys (Macaca mulatta) are reported in which fully automated testing paradigms, afforded by the Language Research Center's Computerized Test System (LRC-CTS), were employed. Performance levels for discrimination learning set, transfer index, and mediational-learning testing were uniformly higher than was predicted from the literature, in contrast to previous reports of compromised learning under similar conditions (automated apparatus, planimetric stimuli, spatial discontiguity between stimuli and response loci). Analyses reveal relatively advanced learning set performance, transfer-index ratios, and positive transfer of learning even at stringent criterion levels. Moreover, the data suggest that rhesus monkeys tested in these experiments exhibit mediational instead of associative learning strategies, as do great apes and in contrast to previous reports of rhesus learning. We argue that the LRC-CTS enhances learning by nonhuman primate subjects, obviating those factors, reported in the literature from experiments in which manual or other automated systems were employed, that compromise learning.     

Socially biased learning among adult cottontop tamarins (Saguinus oedipus)

We presented adult cottontop tamarins (Saguinus oedipus) with a novel foraging task that had been used previously to examine socially biased learning of juvenile observers [Humle & Snowdon, Animal Behaviour 75:267–277, 2008]. The task could be solved in one of two ways, and thus allowed for an analysis of behavioral matching between an observer and a skilled demonstrator (trained to use one of the two methods exclusively). Because the demonstrator was an adult in both this study and the juvenile study, the influence of the observer's age could be isolated and examined, as well as the behavior of demonstrators toward observers of different ages. Our main goals were to (1) compare adults and juveniles acquiring the same task to identify how the age of the observer affects socially biased learning and (2) examine the relationship between socially biased learning and behavioral matching in adults. Although adults spent less time observing the trained demonstrators than did juveniles, the adults were more proficient at solving the task. Furthermore, even though observers did not overtly match the behavior of the demonstrator, observation remained an important factor in the success of these individuals. The findings suggested that adult observers could extract information needed to solve a novel foraging task without explicitly matching the behavior of the demonstrator. Adult observers begged much less than juveniles and demonstrators did not respond to begging from adult. Skill acquisition and the process of socially biased learning are, therefore, age‐dependent and are influenced by the behavioral interactions between observer and demonstrator. To what extent this holds true for other primates or animal species still needs to be more fully investigated and considered when designing experiments and interpreting results. Am. J. Primatol. 72:287–295, 2010. © 2009 Wiley‐Liss, Inc.     

Acoustic facilitation of object movement detection during self-motion

In humans, as well as most animal species, perception of object motion is critical to successful interaction with the surrounding environment. Yet, as the observer also moves, the retinal projections of the various motion components add to each other and extracting accurate object motion becomes computationally challenging. Recent psychophysical studies have demonstrated that observers use a flow-parsing mechanism to estimate and subtract self-motion from the optic flow field. We investigated whether concurrent acoustic cues for motion can facilitate visual flow parsing, thereby enhancing the detection of moving objects during simulated self-motion. Participants identified an object (the target) that moved either forward or backward within a visual scene containing nine identical textured objects simulating forward observer translation. We found that spatially co-localized, directionally congruent, moving auditory stimuli enhanced object motion detection. Interestingly, subjects who performed poorly on the visual-only task benefited more from the addition of moving auditory stimuli. When auditory stimuli were not co-localized to the visual target, improvements in detection rates were weak. Taken together, these results suggest that parsing object motion from self-motion-induced optic flow can operate on multisensory object representations.     

A new perceptual bias reveals suboptimal population decoding of sensory responses

Several studies have reported optimal population decoding of sensory responses in two-alternative visual discrimination tasks. Such decoding involves integrating noisy neural responses into a more reliable representation of the likelihood that the stimuli under consideration evoked the observed responses. Importantly, an ideal observer must be able to evaluate likelihood with high precision and only consider the likelihood of the two relevant stimuli involved in the discrimination task. We report a new perceptual bias suggesting that observers read out the likelihood representation with remarkably low precision when discriminating grating spatial frequencies. Using spectrally filtered noise, we induced an asymmetry in the likelihood function of spatial frequency. This manipulation mainly affects the likelihood of spatial frequencies that are irrelevant to the task at hand. Nevertheless, we find a significant shift in perceived grating frequency, indicating that observers evaluate likelihoods of a broad range of irrelevant frequencies and discard prior knowledge of stimulus alternatives when performing two-alternative discrimination.     

Individual and sex differences in learning abilities of ravens

Behavioral and physiological characteristics of individuals within the same species have been found to be stable across time and contexts. In this study, we investigated individual differences in learning abilities and object and social manipulation to test for consistency within individuals across different tasks. Individual ravens (Corvus corax) were tested in simple color and position discrimination tasks to establish their learning abilities. We found that males were significantly better in the acquisition of the first discrimination task and the object manipulation task, but not in any of the other tasks. Furthermore, faster learners engaged less often in manipulations of conspecifics and exploration of objects to get access to food. No relationship between object and social manipulation and reversal training were found. Our results suggest that individual differences in regard to the acquisition of new tasks may be related to personalities or at least object manipulation in ravens.     

Behavior and neurobehavioral teratology using the ferret

A behavioral profile of the ferret is presented for those who would like to use this animal in behavioral teratology and toxicology, or other disciplines involving behavior. We have reviewed neurobehavioral teratology of lisencephalic ferrets and neuropsychology of ferrets sustaining frontal lesions, as well as most of the studies of "normal" ferret behavior that have appeared in the research literature. Emphasis is placed on discussion of the tests used and how ferrets behaved on them. The behaviors discussed include spatial (maze) learning, delayed response, visual discrimination learning, discrimination learning sets, schedule maintained behavior, shock avoidance learning and spontaneously occurring behaviors, such as ambulation in open field, spontaneous alternation and species specific behaviors. Although the use of the ferret in behavioral experiments is not yet extensive and large gaps exist in our knowledge about the basic functional capacities of this animal, the ferret is unquestionably well suited for behavioral studies.     

An observational learning task using Barnes maze in rats

Observational learning, which modulates one’s own behavior by observing the adaptive behavior of others, is crucial for behaving efficiently in social communities. Although many behavioral experiments have reported observational learning in monkeys and humans, its neural mechanisms are still unknown. In order to conduct neuroscientific researches with recording neural activities, we developed an observational learning task for rats. We designed the task using Barnes circular maze and then tested whether rats (observers) could actually improve their learning by observing the behavior of other rats (models) that had already acquired the task. The result showed that the observer rats, which were located in a metal wire mesh cylinder at the center of the maze and allowed to observe model rats escaping to the goal in the maze, demonstrated significantly faster escape behavior than the model rats. Thus, the present study confirmed that rats can efficiently learn the behavioral task by observing the behavior of other rats; this shows that it is conceivable to elucidate the neural mechanisms of social interaction by analyzing neural activity in observer rats performing the observational learning task.     

Choosing Priority-Setting Criteria for Carcinogens

For priority-setting purposes, simple criteria are needed to estimate, provisionally, the inherent properties of potential carcinogens for which adequate data are not available. Expected utility analysis is used to evaluate three such criteria from a decision-theoretic point of view: (1) the species criterion, which assigns lower priority to experimental than to epidemiological carcinogens, (2) the genotoxicity criterion, which prioritizes substances known to be genotoxic, and (3) the potency criterion, which apportions priorities according to carcinogenic potencies that are derived from animal experiments. The outcome of this analysis is favorable to the potency criterion. It is concluded that considerations of potency should have a much more prominent role than what they have in current regulatory practice.     

Long-term retention and overshadowing of proximal and distal cues following habituation in an object exploration task

The object displacement task is a popular tool used to investigate spatial learning and memory. However, little attention has previously been given to long-term retention of spatial information following habituation to this task. Furthermore, the role of both proximal and distal cues in this type of passive retention of spatial information is controversial. In Study 1, we examined habituation in the object displacement task across 4 days and examined reactivity to spatial change 7 days post-acquisition. We found that rats habituated rapidly to the environment and retained this environment for the 7 days. Furthermore, this experiment shows that both proximal and distal spatial cues are important in the encoding of the environment during object displacement learning task. In Study 2, we examined the effect of overshadowing and demonstrate that proximal visual spatial cues can overshadow distal spatial cues if a conflict arises between both set.     

Simulated self-motion alters perceived time to collision

Many authors have assumed that motor actions required for collision avoidance and for collision achievement (for example, in driving a car or hitting a ball) are guided by monitoring the time to collision (TTC), and that this is done on the basis of moment-to-moment values of the optical variable tau [1] [2] [3]. This assumption has also motivated the search for single neurons that fire when tau is a certain value [4] [5] [6] [7] [8]. Almost all of the laboratory studies and all the animal experiments were restricted to the case of stationary observer and moving object. On the face of it, this would seem reasonable. Even though humans and other animals routinely perform visually guided actions that require the TTC of an approaching object to be estimated while the observer is moving, tau provides an accurate estimate of TTC regardless of whether the approach is produced by self-motion, object-motion or a combination of both. One might therefore expect that judgements of TTC would be independent of self-motion. We report here, however, that simulated selfmotion using a peripheral flow field substantially altered estimates of TTC for an approaching object, even though the peripheral flow field did not affect the value of tau for the approaching object. This finding points to long range interactions between collision-sensitive visual neurons and neural mechanisms for processing self-motion.     

Performance of African elephants (Loxodonta africana) and California sea lions (Zalophus californianus) on a two-choice object discrimination task

This study documents the ability of African elephants (Loxodonta africana) and California sea lions (Zalophus californianus) to perform a two-choice object discrimination task. Both species were able to perform this task. However, California sea lions took fewer trials overall to reach a criterion of 10 consecutively correct responses than did African elephants. The performance of California sea lions did not change significantly during this study. However, African elephants showed a gradual learning of the task, as exhibited by a gradual decrease in the number of trials needed to reach criterion. This performance difference may reflect differences in either visual abilities or cognitive functioning, which in turn may be influenced by either different evolutionary pressures exerted on herbivores and carnivores, or by the context in which visual information is used in the lives of these animals. © 1994 Wiley-Liss, Inc.     

Discrimination reversal learning reveals greater female behavioural flexibility in guppies

Behavioural flexibility allows an animal to adapt its behaviour in response to changes in the environment. Research conducted in primates, rodents and domestic fowl suggests greater behavioural persistence and reduced behavioural flexibility in males. We investigated sex differences in behavioural flexibility in fish by comparing male and female guppies (Poecilia reticulata) in a reversal learning task. Fish were first trained on a colour discrimination, which was learned equally rapidly by males and females. However, once the reward contingency was reversed, females were better at inhibiting the previous response and reached criterion twice as fast as males. When reward reversing was repeated, males gradually reduced the number of errors, and the two sexes had a comparable performance after four reversals. We suggest that sex differences in behavioural flexibility in guppies can be explained in terms of the different roles that males and females play in reproduction.     

Hippocampal Sharp Wave/Ripples during Sleep for Consolidation of Associative Memory

The beneficial effect of sleep on memory has been well-established by extensive research on humans, but the neurophysiological mechanisms remain a matter of speculation. This study addresses the hypothesis that the fast oscillations known as ripples recorded in the CA1 region of the hippocampus during slow wave sleep (SWS) may provide a physiological substrate for long term memory consolidation. We trained rats in a spatial discrimination task to retrieve palatable reward in three fixed locations. Hippocampal local field potentials and cortical EEG were recorded for 2 h after each daily training session. There was an increase in ripple density during SWS after early training sessions, in both trained rats and in rats randomly rewarded for exploring the maze. In rats learning the place -reward association, there was a striking further significant increase in ripple density correlated with subsequent improvements in behavioral performance as the rat learned the spatial discrimination aspect of the task. The results corroborate others showing an experience-dependent increase in ripple activity and associated ensemble replay after exploratory activity, but in addition, for the first time, reveal a clear further increase in ripple activity related to associative learning based on spatial discrimination.     

Reduced expression of the vesicular acetylcholine transporter causes learning deficits in mice

Storage of acetylcholine in synaptic vesicles plays a key role in maintaining cholinergic function. Here we used mice with a targeted mutation in the vesicular acetylcholine transporter (VAChT) gene that reduces transporter expression by 40% to investigate cognitive processing under conditions of VAChT deficiency. Motor skill learning in the rotarod revealed that VAChT mutant mice were slower to learn this task, but once they reached maximum performance they were indistinguishable from wild-type mice. Interestingly, motor skill performance maintenance after 10 days was unaffected in these mutant mice. We also tested whether reduced VAChT levels affected learning in an object recognition memory task. We found that VAChT mutant mice presented a deficit in memory encoding necessary for the temporal order version of the object recognition memory, but showed no alteration in spatial working memory, or spatial memory in general when tested in the Morris water maze test. The memory deficit in object recognition memory observed in VAChT mutant mice could be reversed by cholinesterase inhibitors, suggesting that learning deficits caused by reduced VAChT expression can be ameliorated by restoring ACh levels in the synapse. These data indicate an important role for cholinergic tone in motor learning and object recognition memory.     

Inattentional Blindness and Individual Differences in Cognitive Abilities

People sometimes fail to notice salient unexpected objects when their attention is otherwise occupied, a phenomenon known as inattentional blindness. To explore individual differences in inattentional blindness, we employed both static and dynamic tasks that either presented the unexpected object away from the focus of attention (spatial) or near the focus of attention (central). We hypothesized that noticing in central tasks might be driven by the availability of cognitive resources like working memory, and that noticing in spatial tasks might be driven by the limits on spatial attention like attention breadth. However, none of the cognitive measures predicted noticing in the dynamic central task or in either the static or dynamic spatial task. Only in the central static task did working memory capacity predict noticing, and that relationship was fairly weak. Furthermore, whether or not participants noticed an unexpected object in a static task was only weakly associated with their odds of noticing an unexpected object in a dynamic task. Taken together, our results are largely consistent with the notion that noticing unexpected objects is driven more by stochastic processes common to all people than by stable individual differences in cognitive abilities.     

Discriminative whisking in the head-fixed rat: optoelectronic monitoring during tactile detection and discrimination tasks

We compared whisking movement patterns during acquisition of tactile detection and object discrimination under conditions in which (a) head movements are excluded and (b) exposure to tactile discriminanda is confined to the large, moveable vibrissae (macrovibrissae). We used optoelectronic instrumentation to track the movements of an individual whisker with high spatio-temporal resolution and a testing paradigm, which allowed us to dissociate performance on an "indicator" response (lever pressing) from the rat's "observing" responses (discriminative whisking). We analyzed the relation between discrimination performance and whisking movement patterns in order to clarify the process by which the indicator response comes under the stimulus control of information acquired by the rat's whisking behavior. Whisking patterns over the course of task acquisition differed with task demands. Acquisition of the Detection task was correlated with modulation of only one whisking movement parameter-total number of whisks emitted, and more whisking was seen on trials in which the discriminandum was absent. Discrimination between a sphere and cube differing in size and texture was correlated with a reduction in whisk duration and protraction amplitude and with a shift towards higher whisking frequencies. Our findings confirm previous reports that acquisition of tactile discriminations involves modulation by the animal of both the amount and the type of whisking. In contrast with a previous report (Brecht et al., 1997), they indicate that rats can solve tactile object detection and discrimination tasks (a) using only the large, motile mystacial vibrissae (macrovibrissae) and (b) without engaging in head movements. We conclude that the functional contribution of the macrovibrissae will vary with the nature of the task and the conditions of testing.     

Visual, haptic and cross-modal recognition of objects and scenes.

In this article we review current literature on cross-modal recognition and present new findings from our studies on object and scene recognition. Specifically, we address the questions of what is the nature of the representation underlying each sensory system that facilitates convergence across the senses and how perception is modified by the interaction of the senses. In the first set of our experiments, the recognition of unfamiliar objects within and across the visual and haptic modalities was investigated under conditions of changes in orientation (0 degrees or 180 degrees ). An orientation change increased recognition errors within each modality but this effect was reduced across modalities. Our results suggest that cross-modal object representations of objects are mediated by surface-dependent representations. In a second series of experiments, we investigated how spatial information is integrated across modalities and viewpoint using scenes of familiar, 3D objects as stimuli. We found that scene recognition performance was less efficient when there was either a change in modality, or in orientation, between learning and test. Furthermore, haptic learning was selectively disrupted by a verbal interpolation task. Our findings are discussed with reference to separate spatial encoding of visual and haptic scenes. We conclude by discussing a number of constraints under which cross-modal integration is optimal for object recognition. These constraints include the nature of the task, and the amount of spatial and temporal congruency of information across the modalities.