Contribution of area MT to stereoscopic depth perception: choice-related response modulations reflect task strategy

Due to the diversity of tuning properties in sensory cortex, only a fraction of neurons are engaged in a particular task. Characterizing the tuning properties of neurons that are functionally linked to behavior is essential for understanding how activity is "read out" from sensory maps to guide decisions. We recorded from middle temporal (MT) neurons while monkeys performed a depth discrimination task, and we characterized the linkage between MT responses and behavioral choices. Trial-to-trial response fluctuations of MT neurons with odd-symmetric ("Near," "Far") disparity tuning were predictive of monkeys' choices, whereas responses of neurons with even-symmetric tuning were not. This result cannot be explained by neuronal sensitivity or any other response property of MT neurons that we examined but is simply explained by the task strategy that monkeys learned during training. We suggest that this approach provides a physiological means to explore how task strategies are implemented in the brain.     

Large number discrimination by mosquitofish

Background

Recent studies have demonstrated that fish display rudimentary numerical abilities similar to those observed in mammals and birds. The mechanisms underlying the discrimination of small quantities (<4) were recently investigated while, to date, no study has examined the discrimination of large numerosities in fish.

Methodology/Principal Findings

Subjects were trained to discriminate between two sets of small geometric figures using social reinforcement. In the first experiment mosquitofish were required to discriminate 4 from 8 objects with or without experimental control of the continuous variables that co-vary with number (area, space, density, total luminance). Results showed that fish can use the sole numerical information to compare quantities but that they preferentially use cumulative surface area as a proxy of the number when this information is available. A second experiment investigated the influence of the total number of elements to discriminate large quantities. Fish proved to be able to discriminate up to 100 vs. 200 objects, without showing any significant decrease in accuracy compared with the 4 vs. 8 discrimination. The third experiment investigated the influence of the ratio between the numerosities. Performance was found to decrease when decreasing the numerical distance. Fish were able to discriminate numbers when ratios were 1∶2 or 2∶3 but not when the ratio was 3∶4. The performance of a sample of undergraduate students, tested non-verbally using the same sets of stimuli, largely overlapped that of fish.

Conclusions/Significance

Fish are able to use pure numerical information when discriminating between quantities larger than 4 units. As observed in human and non-human primates, the numerical system of fish appears to have virtually no upper limit while the numerical ratio has a clear effect on performance. These similarities further reinforce the view of a common origin of non-verbal numerical systems in all vertebrates.     

Predicting the frequency of food-related agonism in white-faced capuchin monkeys (Cebus capucinus), using a novel focal-tree method

Food abundance and distribution have played a central role in the conceptual theory of primate socioecology [Janson, Behaviour 105:53-76, 1988; Isbell, Behavioral Ecology 2:143-155, 1991; Sterck et al., Behavioral Ecology and Sociobiology 41:291-309, 1997; van Schaik, In: Standen V, Foley RA, editors, Comparative Socioecology. Oxford: Blackwell. p 195-218, 1989]. This theory predicts that agonistic ("contest") competition should occur when food is distributed in discrete, defensible patches; in contrast, when food sources are distributed uniformly or randomly, non-agonistic ("scramble") competition is expected. Primatologists usually measure resource density and patchiness from a botanical perspective, ignoring the biology of the animal being studied. Such an approach may be irrelevant in terms of how animals view the dispersion of resources. Using a novel focal-tree method that measures resource availability on a scale that is both spatially and temporally relevant to the animal under investigation, we take a cost-benefit approach to predict the frequency of food-related agonism in white-faced capuchin monkeys (Cebus capucinus) from 11 ecological and social variables. We retained four variables in the regression model: two representing the opportunity for aggression (i.e., feeding bout length and the number of feeding adult females), and two representing opportunity costs (i.e., fruit abundance and the number of potential feeding sites in the focal tree). The results of this study indicate that the amount of food-related aggression in white-faced capuchins can be predicted by variables representing the costs and benefits of contesting a food resource.     

Teams in animal societies

We review the existence of teams in animal societies. Teamshave previously been dismissed in all but a tiny minority ofinsect societies. "Team" is a term not generally used in studiesof vertebrates. We propose a new rigorous definition of a teamthat may be applied to both vertebrate and invertebrate societies.We reconsider what it means to work as a team or group andsuggest that there are many more teams in insect societies than previously thought. A team task requires different subtasksto be performed concurrently for successful completion. Thereis a division of labor within a team. Contrary to previousreviews of teams in social insects, we do not constrain teamsto consist of members of different castes and argue that teammembers may be interchangeable. Consequently, we suggest thata team is simply the set of individuals that performs a teamtask. We contrast teams with groups and suggest that a grouptask requires the simultaneous performance and cooperationof two or more individuals for successful completion. In agroup, there is no division of labor—each individual performs the same task. We also contrast vertebrate and invertebrateteams and find that vertebrate teams tend to be associatedwith hunting and are based on individual recognition. Invertebrateteams occur in societies characterized by a great deal of redundancy,and we predict that teams in insect societies are more likelyto be found in large polymorphic ("complex") societies thanin small monomorphic ("simple") societies.     

Comparisons of likelihood and machine learning methods of individual classification

Classification methods used in machine learning (e.g., artificial neural networks, decision trees, and k-nearest neighbor clustering) are rarely used with population genetic data. We compare different nonparametric machine learning techniques with parametric likelihood estimations commonly employed in population genetics for purposes of assigning individuals to their population of origin ("assignment tests"). Classifier accuracy was compared across simulated data sets representing different levels of population differentiation (low and high F(ST)), number of loci surveyed (5 and 10), and allelic diversity (average of three or eight alleles per locus). Empirical data for the lake trout (Salvelinus namaycush) exhibiting levels of population differentiation comparable to those used in simulations were examined to further evaluate and compare classification methods. Classification error rates associated with artificial neural networks and likelihood estimators were lower for simulated data sets compared to k-nearest neighbor and decision tree classifiers over the entire range of parameters considered. Artificial neural networks only marginally outperformed the likelihood method for simulated data (0-2.8% lower error rates). The relative performance of each machine learning classifier improved relative likelihood estimators for empirical data sets, suggesting an ability to "learn" and utilize properties of empirical genotypic arrays intrinsic to each population. Likelihood-based estimation methods provide a more accessible option for reliable assignment of individuals to the population of origin due to the intricacies in development and evaluation of artificial neural networks.     

Individuality in nest building: do southern masked weaver (Ploceus velatus) males vary in their nest-building behaviour?

This study investigated how infant pigtailed macaque monkeys performed on two separate learning assessments, two-object discrimination/reversal and Hamilton search learning. Although the learning tasks have been tested on several species, including non-human primates, there have been no normative results reported for young macaque monkeys. The present study provides normative results for these learning tasks in very young captive pigtailed macaques and investigates the degree to which performances on these assessments are related. In addition, an error analysis was conducted to understand the choice patterns of the animals on each task. It was found that males took longer to reach criterion than females on the two-object reversal task. Performance and latency on the discrimination task predicted performance and latency on the reversal task. Performance on Hamilton Search Set-Breaking negatively predicted performance on the later Hamilton Search Forced Set-Breaking task. Finally, latency on reversal significantly predicted the latency on the Hamilton search task. These data provide strong evidence of a relationship between performance on discrimination and reversal. This study shows that, otherwise, each task assesses a different cognitive function.     

False-positive and false-negative proficiency test results in cytology

Proficiency tests in cytology classify a certain proportion of cytologists inaccurately. Some competent cytologists fail during the testing procedure ("false-negative proficiency test" or "type I error") while some individuals who should fail do pass the test ("false-positive proficiency test" or "type II error"). In other words, success or failure during proficiency testing may be the consequence of statistical chance. Calculations based on the binomial distribution are presented to show the seriousness of this problem. The analysis demonstrated that increasing the number of slides in the test sets does not necessarily improve the accuracy of the test. For instance, on the 90% ("borderline competent") level, raising the number of slides in one test set from 10 to 20 reduced the accuracy of the test by 6%.     

Language models based on Hebbian cell assemblies.

This paper demonstrates how associative neural networks as standard models for Hebbian cell assemblies can be extended to implement language processes in large-scale brain simulations. To this end the classical auto- and hetero-associative paradigms of attractor nets and synfire chains (SFCs) are combined and complemented by conditioned associations as a third principle which allows for the implementation of complex graph-like transition structures between assemblies. We show example simulations of a multiple area network for object-naming, which categorises objects in a visual hierarchy and generates different specific syntactic motor sequences ("words") in response. The formation of cell assemblies due to ongoing plasticity in a multiple area network for word learning is studied afterwards. Simulations show how assemblies can form by means of percolating activity across auditory and motor-related language areas, a process supported by rhythmic, synchronized propagating waves through the network. Simulations further reproduce differences in own EEG&MEG experiments between responses to word- versus non-word stimuli in human subjects.     

Determining the number of factors in P-technique factor analysis

Determining the number of factors is a critical first step in exploratory factor analysis. Although various criteria and methods for determining the number of factors have been evaluated in the usual between-subjects R-technique factor analysis, there is still question of how these methods perform in within-subjects P-technique factor analysis. A novel feature of P-technique data is that observations are usually sequentially dependent in some way. The current study evaluates 10 criteria for determining the number of factors for data simulated to resemble intensive repeated-measures data for which P-technique is usually applied. The number of factors, loading size, observed-to-latent ratio, serial-dependency, and sample size were simulation design factors with conditions simulated to resemble P-technique data. The methods are compiled from various statistical techniques and have been demonstrated in previous R-technique simulations. Finally, a real data example demonstrates applying the acceleration factor method to several time series data sets.     

Tracking of food quantity by coyotes (Canis latrans)

Previous studies have demonstrated that Weber's Law mediates quantitative discrimination abilities across various species. Here, we tested coyotes’ (Canis latrans) ability to discriminate between various quantities of food and investigated whether this ability conforms to predictions of Weber's Law. We demonstrate herein that coyotes are capable of reliably discriminating large versus small quantities of discrete food items. As predicted by Weber's Law, coyotes’ quantitative discrimination abilities are mediated by the ratio between the large and small quantities of food and exhibit scalar variability. Furthermore, in this task coyotes were not discriminating large versus small quantities based on olfactory cues alone.     

The model of the reward choice basing on the theory of reinforcement learning

We developed the model of alimentary instrumental conditioned bar-pressing reflex for cats making a choice between either immediate small reinforcement ("impulsive behavior") or delayed more valuable reinforcement ("self-control behavior"). Our model is based on the reinforcement learning theory. We emulated dopamine contribution by discount coefficient of this theory (a subjective decrease in the value of a delayed reinforcement). The results of computer simulation showed that "cats" with large discount coefficient demonstrated "self-control behavior"; small discount coefficient was associated with "impulsive behavior". This data are in agreement with the experimental data indicating that the impulsive behavior is due to a decreased amount of dopamine in striatum.     

Inactivation in ShakerB K+ channels: a test for the number of inactivating particles on each channel.

Fast inactivation in ShakerB K channels results from pore-block caused by "ball peptides" attached to the inner part of each K channel. We have examined the question of how many functional inactivating balls are on each channel and how this number affects inactivation and recovery from inactivation. To that purpose we expressed ShakerB in the insect cell line Sf9 and gradually removed inactivation by perfusing the cell interior with the hydrolytic enzyme papain under whole cell patch clamp. Inactivation slows down as the balls are removed by an amount consistent with the presence of four balls on each channel. Recovery from inactivation has the same time course early and late in papain action; it does not depend on the number of balls remaining on the channel, consistent with the idea that reinactivation is not significant during recovery from inactivation. Our conclusion is that ShakerB has four ball peptides, each capable of causing inactivation. Statistically, the balls are identical and independent. The stability of N-type inactivation by the remaining balls is not appreciably affected by removing some of the balls from a channel.     

Adaptive value of host discrimination in parasitoids: when host defences are very costly

Host acceptance decision in parasitic wasps strongly depends on the parasitism status of the encountered host. In solitary species, a host only allows the development of a single parasitic larva and then, any oviposition in an already parasitised host leads to larval competition and loss of offspring. Females of many parasitoid species are able to discriminate between parasitised hosts and healthy ones. However, the host discrimination process may require more time than oviposition, exposing the wasp to high risks when the host has efficient defences. Consequently, depending on the degree of success of the host defence, the cost of host inspection for discrimination can outweigh the benefit of superparasitism avoidance. In the present paper, a theoretical approach was developed for determining how host defences may affect optimal host acceptance behaviour in parasitoids. The present model compares the lifetime reproductive success over the strategy used, discrimination and no-discrimination: a discriminating wasp sets a relatively greater value in its current oviposition, while a non-discriminating female sets a greater value in its own survival and future reproduction. The model predicts that depending on physiological state variables and environmental state variables, the optimal policy is not discriminating. Our results suggest that the low discriminating ability observed in some parasitic wasps could probably be an evolutionary response to host defences pressure.     

Information, discrimination and divergence in cytology. VI. Biases and errors of measurement in small samples.

Total discrimination and total divergence have been shown to be useful measures of performance in diagnostic cytology. The sample size, Ns (observed number of cytology-histology pairs, essential components of a confusion matrix), may be small for the comparison of two or more laboratories or periodic quality control using observed values. From actual data from previous reports in this series, the best estimation of the confusion matrix of a population was obtained by fitting a Gaussian-type curve after pseudoscalar transform of ranks (row and column numbers). Small sample confusion matrices were generated by Monte Carlo simulation to 2.5 x 10(-7) resolution. To keep measurement biases within +/- 0.5 decits, we found that 100-200 samples of cytology-histology pairs were required in the best classifications of three, four and five category-states. At these sample sizes, measurement errors (standard errors) were also contained within +/- 0.5 decits. This study also confirmed that previously reported overestimated propagated errors in small samples were in fact overestimation and that their use for testing a null hypothesis was valid. The number of samples with indefinable statistics due to a zero denominator can be as high as 30% when the sample sizes are 500 for three, four and five category-state classifications. Biases due to small samples were positive for most category-states except for the optimum three category-states, in which bias changed to negative ("bias inversion"), and observed errors of discrimination and divergence paradoxically decreased as Ns decreased ("error-sample paradox") for a small sample size (Ns less than 700).(ABSTRACT TRUNCATED AT 250 WORDS)     

Categorization training results in shape- and category-selective human neural plasticity

Object category learning is a fundamental ability, requiring the combination of "bottom-up" stimulus-driven with "top-down" task-specific information. It therefore may be a fruitful domain for study of the general neural mechanisms underlying cortical plasticity. A simple model predicts that category learning involves the formation of a task-independent shape-selective representation that provides input to circuits learning the categorization task, with the computationally appealing prediction of facilitated learning of additional, novel tasks over the same stimuli. Using fMRI rapid-adaptation techniques, we find that categorization training (on morphed "cars") induced a significant release from adaptation for small shape changes in lateral occipital cortex irrespective of category membership, compatible with the sharpening of a representation coding for physical appearance. In contrast, an area in lateral prefrontal cortex, selectively activated during categorization, showed sensitivity posttraining to explicit changes in category membership. Further supporting the model, categorization training also improved discrimination performance on the trained stimuli.     

The effect of auditory distractors on song discrimination in male canaries (Serinus canaria)

Male songbirds such as canaries produce complex learned vocalizations that are used in the context of mate attraction and territory defense. Successful mate attraction or territorial defense requires that a bird be able to recognize individuals based on their vocal performance and identify these songs in a noisy background. In order to learn more about how birds are able to solve this problem, we investigated, with a two-alternative choice procedure, the ability of adult male canaries to discriminate between conspecific song segments from two different birds and to maintain this discrimination when conspecific songs are superimposed with a variety of distractors. The results indicate that male canaries have the ability to discriminate, with a high level of accuracy song segments produced by two different conspecific birds. Song discrimination was partially maintained when the stimuli were masked by auditory distractors, but the accuracy of the discrimination progressively declined as a function of the number of masking distractors. The type of distractor used in the experiments (other conspecific songs or different types of artificial white noise) did not markedly affect the rate of deterioration of the song discrimination. These data indicate that adult male canaries have the perceptual abilities to discriminate and selectively attend to one ongoing sound that occurs simultaneously with one or more other sounds. The administration of a noradrenergic neurotoxin did not impair markedly the discrimination learning abilities although the number of subjects tested was too small to allow any firm conclusion. In these conditions, however, the noradrenergic lesion significantly increased the number failures to respond in the discrimination learning task suggesting a role, in canaries, of the noradrenergic system in some attentional processes underlying song learning and processing.     

Comparative and functional morphology of musculus canalis ani in tetrapod mammals and primates]

Comparative anatomy of structure and function of the M. canalis ani in tetrapode mammals and primates is described for the first time. The muscle itself lies on the sphincter ani internus in the area between the anorectal ("pectinate") and anocutaneal ("white") lines and its circumference is intact around the entire anal canal. The canalis ani muscle orginates from the superior part of the sphincter ani internus and concomitantly receives additional fibers from the longitudinal muscle. Caudally the muscle dips back into the sphincter ani internus and, at the same time, a small portion of the fibers go to the longitudinal muscle and, likewise, a portion also sets itself on the perinaal skin. On the basis of its morphological relationship to the convoluted vessels of the rectal venous plexus, the canalis ani muscle appears to be able to complete the closing of the anus in the continence phase to such an extent that a complete closing of the anal lumen is guaranted.     

Effect of verbal reinforcement on evoked cortical activity

Adult healthy subjects did not manifest any difference in latency and amplitude of the wave P300 elicited by a positive ("good") and negative ("error") reinforcing stimuli. After the negative reinforcement, the P300 wave amplitude decreases in response to the standard stimulus (light bars) and increases to a lesser degree in response to test stimuli (the same bars but presented with different pauses). In the processes of learning to assess time microintervals in comparison with the standard, the latency of wave P300 to the test stimuli shortens. It is suggested that formation and consolidation of feedback connection elaborated with the participation of a reinforcing verbal stimulus constitute the physiological basis for learning of comparative assessment of time microintervals.