Contextual modulation of behavioral choice

We review the influence of context on behavioral choice. Context can refer to external (environmental) factors such as the season or presence of predators and it can also refer to the internal or behavioral state of an animal. Usually, animals make decisions in the midst of other ongoing behaviors. We discuss recent findings on the impact of both types of contexts, focusing on how context gets encoded at the intersection between the sensory and motor systems, emphasizing the role of neuromodulators. We also review recent technological advances that have made feasible the exploration of neural correlates of decision making in freely moving, behaving animals.     

Contextual modulation outside of awareness

Contextual effects are ubiquitous in vision and reveal fundamental principles of sensory coding. Here, we demonstrate that an oriented surround grating can affect the perceived orientation of a central test grating even when backward masking of the surround prevents its orientation from being consciously perceived. The effect survives introduction of a gap between test and surround of over a degree even under masking, suggesting either that contextual information can effectively propagate across early visual cortex in the absence of awareness of the signaled context or that it can proceed undetected to higher processing levels at which such horizontal propagation may not be necessary. The effect under masking also shows partial interocular transfer, demonstrating processing of orientation by binocular neurons in visual cortex in the absence of conscious orientation perception. This pattern of results is consistent with the suggestion that simultaneous orientation contrast is mediated at multiple levels of the visual processing hierarchy, and it supports the view that propagation of signals to and, possibly, back from higher visual areas is necessary for conscious perception.     

Contextual modulation of androgen effects on agonistic interactions

Seasonal changes in steroid hormones are known to have a major impact on social behavior, but often are quite sensitive to environmental context. In the bi-directionally sex changing fish, Lythrypnus dalli, stable haremic groups exhibit baseline levels of interaction. Status instability follows immediately after male removal, causing transiently elevated agonistic interactions and increase in brain and systemic levels of a potent fish androgen, 11-ketotestosterone (KT). Coupling KT implants with a socially inhibitory environment for protogynous sex change induces rapid transition to male morphology, but no significant change in social behavior and status, which could result from systemically administered steroids not effectively penetrating into brain or other tissues. Here, we first determined the degree to which exogenously administered steroids affect the steroid load within tissues. Second, we examined whether coupling a social environment permissive to sex change would influence KT effects on agonistic behavior. We implanted cholesterol (Chol, control) or KT in the dominant individual (alpha) undergoing sex change (on d0) and determined the effects on behavior and the degree to which administered steroids altered the steroid load within tissues. During the period of social instability, there were rapid (within 2 h), but transient effects of KT on agonistic behavior in alphas, and secondary effects on betas. On d3 and d5, all KT, but no Chol, treated females had male typical genital papillae. Despite elevated brain and systemic KT 5 days after implant, overall rates of aggressive behavior remained unaffected. These data highlight the importance of social context in mediating complex hormone–behavior relationships.     

Modelling face recognition.

Much early work in the psychology of face processing was hampered by a failure to think carefully about task demands. Recently our understanding of the processes involved in the recognition of familiar faces has been both encapsulated in, and guided by, functional models of the processes involved in processing and recognizing faces. The specification and predictive power of such theory has been increased with the development of an implemented model, based upon an 'interactive activation and competition' architecture. However, a major deficiency in most accounts of face processing is their failure to spell out the perceptual primitives that form the basis of our representations for faces. Possible representational schemes are discussed, and the potential role of three-dimensional representations of the face is emphasized.     

Contextual modulation of visuomotor associations in bumble-bees (Bombus terrestris)

We performed the following experiment to investigate whether contextual cues can prevent interference during the acquisition of potentially competing visuomotor associations. In the bumble-bee (Bombus terrestris). Bees discriminated between horizontally and vertically orientated gratings of black and white stripes in order to reach a feeder and between different diagonally orientated gratings to gain access to their nest. Once bees were well trained on these two tasks, the discrimination task at the nest was changed so that bees had to distinguish between horizontal and vertical gratings at both sites. Whereas they still approached the horizontal grating to reach food, they now had to approach a vertical grating in order to return to their nest. The new task was learnt rapidly. Errors at the feeder did not increase during or after the acquisition of this potentially competing behaviour at the nest entrance. For a brief period during acquisition, bees showed some hesitation at the feeder and hovered for slightly longer before choosing between horizontals and verticals. After acquisition was complete, bees showed a slight increase in their preference for verticals over a more ambiguous stimulus of an array of dots. These findings are consistent with the hypothesis that different contextual signals are associated with approaching the nest or approaching the feeder, and that these contextual signals facilitate learnt associations between orientation detectors and motor commands.     

Biased face recognition in the Faith Game

Several studies have indicated that people are able to memorize the face of a cheater more accurately than that of a noncheater, but some contradictory findings have also been reported. Because most previous studies focused on memory for the faces of cheaters who break social contracts, the consequence for the subjects of their cheating was unclear. In our study, participants were asked to decide whether they trusted persons depicted in photographs to give them money using two sessions of the Faith Game. The participants tended to not increase their trust in the individuals, depicted in photographs, who had altruistically given money to them previously. However, participants recognized nonaltruists who had not shared money and, during the second session, rescinded the trust that they had previously placed in them. This suggests that bias in face recognition is not restricted to the recognition level, as previous studies have suggested, but also operates at the behavioral level and functions to facilitate the avoidance of persons who have caused some disadvantage in a previous interaction, rather than to facilitate new relationships with altruists by enhancing recognition of their faces.     

The significance of hair for face recognition

Hair is a feature of the head that frequently changes in different situations. For this reason much research in the area of face perception has employed stimuli without hair. To investigate the effect of the presence of hair we used faces with and without hair in a recognition task. Participants took part in trials in which the state of the hair either remained consistent (Same) or switched between learning and test (Switch). It was found that in the Same trials performance did not differ for stimuli presented with and without hair. This implies that there is sufficient information in the internal features of the face for optimal performance in this task. It was also found that performance in the Switch trials was substantially lower than in the Same trials. This drop in accuracy when the stimuli were switched suggests that faces are represented in a holistic manner and that manipulation of the hair causes disruption to this, with implications for the interpretation of some previous studies.     

Contextual modulation of V1 receptive fields depends on their spatial symmetry

The apparent receptive field characteristics of sensory neurons depend on the statistics of the stimulus ensemble—a nonlinear phenomenon often called contextual modulation. Since visual cortical receptive fields determined from simple stimuli typically do not predict responses to complex stimuli, understanding contextual modulation is crucial to understanding responses to natural scenes. To analyze contextual modulation, we examined how apparent receptive fields differ for two stimulus ensembles that are matched in first- and second-order statistics, but differ in their feature content: one ensemble is enriched in elongated contours. To identify systematic trends across the neural population, we used a multidimensional scaling method, the Procrustes transformation. We found that contextual modulation of receptive field components increases with their spatial extent. More surprisingly, we also found that odd-symmetric components change systematically, but even-symmetric components do not. This symmetry dependence suggests that contextual modulation is driven by oriented On/Off dyads, i.e., modulation of the strength of intracortically-generated signals. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A testing time for face recognition technology

Face recognition continues to make progress, with significant numbers of players now having commercial products. But the sector needs to address scalability, privacy and accuracy problems to become a truly dominant force in the industry.     

Quaternion-based discriminant analysis method for color face recognition

Pattern recognition techniques have been used to automatically recognize the objects, personal identities, predict the function of protein, the category of the cancer, identify lesion, perform product inspection, and so on. In this paper we propose a novel quaternion-based discriminant method. This method represents and classifies color images in a simple and mathematically tractable way. The proposed method is suitable for a large variety of real-world applications such as color face recognition and classification of the ground target shown in multispectrum remote images. This method first uses the quaternion number to denote the pixel in the color image and exploits a quaternion vector to represent the color image. This method then uses the linear discriminant analysis algorithm to transform the quaternion vector into a lower-dimensional quaternion vector and classifies it in this space. The experimental results show that the proposed method can obtain a very high accuracy for color face recognition.