Despite considerable evidence that neural activity in monkeys reflects various aspects of face perception, relatively little is known about monkeys’ face processing abilities. Two characteristics of face processing observed in humans are a subordinate-level entry point, here, the default recognition of faces at the subordinate, rather than basic, level of categorization, and holistic effects, i.e. perception of facial displays as an integrated whole. The present study used an adaptation paradigm to test whether untrained rhesus macaques (Macaca mulatta) display these hallmarks (...) of face processing. In experiments 1 and 2, macaques showed greater rebound from adaptation to conspecific faces than to other animals at the individual or subordinate level. In experiment 3, exchanging only the bottom half of a monkey face produced greater rebound in aligned than in misaligned composites, indicating that for normal, aligned faces, the new bottom half may have influenced the perception of the whole face. Scan path analysis supported this assertion: during rebound, fixation to the unchanged eye region was renewed, but only for aligned stimuli. These experiments show that macaques naturally display the distinguishing characteristics of face processing seen in humans and provide the first clear demonstration that holistic information guides scan paths for conspecific faces. (shrink)
manganese (Mn2+) enhanced MRI (MEMRI) to study neuronal connectivity in vivo opens the possibility to these studies. However, several drawbacks exist that challenge its applicability. High Mn2+ concentrations produce cytotoxic effects that can perturb the circuits under study. In the other hand, the MR signal is..
In-vivo phenotyping of genetically engineered mouse models for amyotrophic lateral sclerosis is established by combining BT-MRI and CASL G. Vanhoutte1, E. Storkebaum2, P. Carmeliet2, A. Van der Linden1.
We report and compare the performance of different learning algorithms based on data from cortical recordings. The task is to predict the orientation of visual stimuli from the activity of a population of simultaneously recorded neurons. We compare several ways of improving the coding of the input (i.e., the spike data) as well as of the output (i.e., the orientation), and report the results obtained using different kernel algorithms.
Asif A. Ghazanfar,1,3,* Hjalmar K. Turesson,1,3 statistical pattern recognition [16, 17] and psychophys- Joost X. Maier,1 Ralph van Dinther,2 ics [13, 18–23] have suggested that formants are signif- Roy D. Patterson,2 and Nikos K. Logothetis1 icant contributors to these indexical cues. It is likely, 1Max Planck Institute for Biological Cybernetics then, that detecting formants could have provided 72076 Tuebingen ancestral primates with indexical cues necessary for Germany navigating the complex social interactions that are the 2Centre for the Neural Basis of (...) Hearing essence of primate societies. One important indexical Department of Physiology cue is body size. Formant cues related to body size University of Cambridge could be used by monkeys to determine the sex (in sex- CB2 3EG Cambridge ually dimorphic species), degree of potential threat (e.g., United Kingdom whether a competitor is larger or smaller), and/or age of an individual, as such cues do for human listeners [13, 18, 20, 21]. Summary Formants are the result of acoustic ﬁltering by the supralaryngeal vocal tract—the nasal and oral cavities Vocal-tract resonances (or formants) are acoustic sigabove the vocal folds. During vocal production, pulses natures in the voice and are related to the shape and of air generated by the rapid movement of the vocal length of the vocal tract. Formants play an important folds produce an acoustic signal. The frequency of these role in human communication, helping us not only to pulses—the glottal-pulse rate—determines the fundadistinguish several different speech sounds , but mental frequency of the signal, which in turn is perceived also to extract important information related to the as pitch. As the signal passes through the supralaryngphysical characteristics of the speaker, so-called ineal vocal tract, it excites resonances, resulting in the dexical cues. How did formants come to play such an enhancement of particular frequency bands; these are important role in human vocal communication? One the formants.. (shrink)
c Ralph Mason -- 199. A New Frontier for Proton MRI: Quantitative Tissue Oximetry g f e d c Ralph P. Mason -- 200. S-GalTM, a Novel 1H MRI Reporter for b-Galactosidase g f e d c John Chen -- 201. Myeloperoxidase-mediated activation of paramagnetic imaging g f e d..
Der vorliegende Band enthält die Zusammenfassungen der Beiträge zur 49. Tagung experimentell arbeitender Psychologen (TeaP), die vom 26. bis 28. März 2007 in Trier stattfindet. Dies ist das zweite Mal, dass diese Tagung an der Universität Trier durchgeführt wird, denn bereits 1982 – also vor 25 Jahren – konnte sie in Trier ausgerichtet werden.
Accumulating evidence indicates that control mechanisms are not tightly bound to conscious perception since both conscious and unconscious information can trigger control processes, probably through the activation of higher-order association areas like the prefrontal cortex. Studying the modulation of control-related prefrontal signals in a microscopic, neuronal level during conscious and unconscious neuronal processing and under control-free conditions could provide an elementary understanding of these interactions. Here we performed extracellular electrophysiological recordings in the macaque lateral prefrontal cortex (LPFC) during monocular physical (...) alternation (PA) and binocular flash suppression (BFS) and studied the local scale relationship between beta (15-30Hz) oscillations, a rhythmic signal believed to reflect the current sensory, motor or cognitive state (status-quo),and conscious or unconscious neuronal processing. First, we show that beta oscillations are observed in the LPFC during resting state. Both PA and BFS had a strong impact on the power of this spontaneous rhythm with the modulation pattern of beta power being identical across these two conditions. Specifically, both perceptual dominance and suppression of local neuronal populations in BFS were accompanied by a transient beta desynchronization followed by beta activity rebound, a pattern also observed when perception occurred without any underlying visual competition in PA. These results indicate that under control-free conditions, at least one rhythmic signal known to reflect control processes in the LPFC (i.e. beta oscillations) is not obstructed by local neuronal, and accordingly perceptual, suppression, thus being independent from temporally co-existing conscious and unconscious local neuronal representations. Future studies could reveal the additive effects of motor or cognitive control demands on prefrontal beta oscillations during conscious and unconscious processing. (shrink)
Perceptual bistability arises when two conflicting interpretations of an ambiguous stimulus or images in binocular rivalry (BR) compete for perceptual dominance. From a computational point of view competition models based on cross-inhibition and adaptation have shown that noise is a crucial force for rivalry and operates in balance with adaptation in order to explain the observed alternations in perception. In particular, noise-driven transitions and adaptation-driven oscillations define two dynamical regimes and the system operates near its boundary. In order to gain (...) insights into the microcircuit dynamics mediating spontaneous perceptual alternations we used a reduced recurrent attractor-based biophysically realistic spiking network well known for working memory, attention and decision-making, where a spike-frequency adaptation mechanism is implemented to account for perceptual bistability. We, thus, derived a consistently reduced four-variable population rate model using mean-field techniques and tested it on BR data collected from human subjects. Our model accounts for experimental data parameters such as time dominance, coefficient of variation and gamma distribution. In addition, we show that our model also operates on the boundary between noise and adaptation and agrees with Levelt’s second revised and fourth propositions. These results show for the first time that a consistent reduction of a biophysically realistic spiking network of integrate and fire neurons with spike frequency adaptation could account for BR. Moreover, we demonstrate that BR can be explained only through the dynamics of the competing neuronal pools, without taking into account the adaptation of inhibitory interneurons..However, adaptation of interneurons affects the optimal parametric space of the system, by decreasing the overall adaptation necessary for the bifurcation to occur. (shrink)
Background: Continuous viewing of ambiguous patterns is characterized by wavering perception that alternates between two or more equally valid visual solutions. However, when such patterns are viewed intermittently, either by repetitive presentation or by periodic closing of the eyes, perception can become locked or "frozen" in one configuration for several minutes at a time. One aspect of this stabilization is the possible existence of a perceptual memory that persists during periods in which the ambiguous stimulus is absent. Here, we use (...) a novel paradgim of temporally interleaved ambiguous stimuli to explore the nature of this memory, with particular regard to its potential impact on perceptual organization. Results: We found that the persistence of a perceptual configuration was robust to interposed visual patterns and, further, that at least three ambiguous patterns, when interleaved in time, could undergo parallel, stable time courses. Then, using an interleaved presentation paradigm, we established that the occasional reversal in one pattern could be coupled with that of its interleaved counterpart, and that this coupling was a function of the structural similarity between the patterns. Conclusions: We postulate that the stabilization observed with repetitive presentation of ambiguous patterns can be at least partially accounted for by processes that retain a recent perceptual interpretation, and we speculate that such memory may be important in natural vision. We further propose tha the interleaved paradigm introduced here may be of great value to gauge aspects of stimulus similarity that appeal to particular mechanisms of perceptual organization. (shrink)
Correspondence should be addressed to David A. Leopold email@example.comDuring the viewing of certain patterns, widely known as ambiguous or puzzle figures, perception lapses into a sequence of spontaneous alternations, switching every few seconds between two or more visual interpretations of the stimulus. Although their nature and origin remain topics of debate, these stochastic switches are generally thought to be the automatic and inevitable consequence of viewing a pattern without a unique solution. We report here that in humans such perceptual alternations (...) can be slowed, and even brought to a standstill, if the visual stimulus is periodically removed from view. We also show, with a visual illusion, that this stabilizing effect hinges on perceptual disappearance rather than on actual removal of the stimulus. These findings indicate that uninterrupted subjective perception of an ambiguous pattern is required for the initiation of the brain-state changes underlying multistable vision.Visual perception involves coordination between sensory sampling of the world and active interpretation of the sensory data. Human perception of objects and scenes is normally stable and robust, but it falters when one is presented with patterns that are inherently ambiguous or contradictory. Under such conditions, vision lapses into a chain of continually alternating percepts, whereby a viable visual interpretation dominates for a few seconds and is then replaced by a rival interpretation. This multistable vision, or 'multistability', is thought to result from destabilization of fundamental visual mechanisms, and has offered valuable insights into how sensory patterns are actively organized and interpreted in the brain1, 2. Despite a great deal of recent research and interest in multistable perception, however, its neurophysiological underpinnings remain poorly understood. Physiological studies have suggested that disambiguation of ambiguous patterns. (shrink)
Traditional explanations of multistable visual phenomena (e.g. ambiguous figures, perceptual rivalry) suggest that the basis for spontaneous reversals in perception lies in antagonistic connectivity within the visual system. In this review, we suggest an alternative, albeit speculative, explanation for visual multistability – that spontaneous alternations reflect responses to active, programmed events initiated by brain areas that integrate sensory and non-sensory information to coordinate a diversity of behaviors. Much evidence suggests that perceptual reversals are themselves more closely related to the expression (...) of a behavior than to passive sensory responses: (1) they are initiated spontaneously, often voluntarily, and are influenced by subjective variables such as attention and mood; (2) the alternation process is greatly facilitated with practice and compromised by lesions in non-visual cortical areas; (3) the alternation process has temporal dynamics similar to those of spontaneously initiated behaviors; (4) functional imaging reveals that brain areas associated with a variety of cognitive behaviors are specifically activated when vision becomes unstable. In this scheme, reorganizations of activity throughout the visual cortex, concurrent with perceptual reversals, are initiated by higher, largely non-sensory brain centers. Such direct intervention in the processing of the sensory input by brain structures associated with planning and motor programming might serve an important role in perceptual organization, particularly in aspects related to selective attention. (shrink)