Residual attention guidance in blindsight monkeys watching complex natural scenes

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Highlights? This study quantitatively analyzes blindsight in natural vision for the first time ? Monkeys with V1 lesion are attracted to salient objects in their lesioned visual field ? Motion, intensity, and color—but not orientation—salience drive blindsight attention ? New laboratory experiments with color stimuli confirm the natural vision findings     

Processing of complex stimuli and natural scenes in the auditory cortex

Neuronal responses in auditory cortex show a fascinating mixture of characteristics that span the range from almost perfect copies of physical aspects of the stimuli to extremely complex context-dependent responses. Fast, highly stimulus-specific adaptation and slower plastic mechanisms work together to constantly adjust neuronal response properties to the statistics of the auditory scene. Evidence with converging implications suggests that the neuronal activity in primary auditory cortex represents sounds in terms of auditory objects rather than in terms of invariant acoustic features.     

Mechanisms for allocating auditory attention: an auditory saliency map

Our nervous system is confronted with a barrage of sensory stimuli, but neural resources are limited and not all stimuli can be processed to the same extent. Mechanisms exist to bias attention toward the particularly salient events, thereby providing a weighted representation of our environment. Our understanding of these mechanisms is still limited, but theoretical models can replicate such a weighting of sensory inputs and provide a basis for understanding the underlying principles. Here, we describe such a model for the auditory system-an auditory saliency map. We experimentally validate the model on natural acoustical scenarios, demonstrating that it reproduces human judgments of auditory saliency and predicts the detectability of salient sounds embedded in noisy backgrounds. In addition, it also predicts the natural orienting behavior of naive macaque monkeys to the same salient stimuli. The structure of the suggested model is identical to that of successfully used visual saliency maps. Hence, we conclude that saliency is determined either by implementing similar mechanisms in different unisensory pathways or by the same mechanism in multisensory areas. In any case, our results demonstrate that different primate sensory systems rely on common principles for extracting relevant sensory events.     

A saliency-based bottom-up visual attention model for dynamic scenes analysis

This work proposes a model of visual bottom-up attention for dynamic scene analysis. Our work adds motion saliency calculations to a neural network model with realistic temporal dynamics [(e.g., building motion salience on top of De Brecht and Saiki Neural Networks 19:1467–1474, (2006)]. The resulting network elicits strong transient responses to moving objects and reaches stability within a biologically plausible time interval. The responses are statistically different comparing between earlier and later motion neural activity; and between moving and non-moving objects. We demonstrate the network on a number of synthetic and real dynamical movie examples. We show that the model captures the motion saliency asymmetry phenomenon. In addition, the motion salience computation enables sudden-onset moving objects that are less salient in the static scene to rise above others. Finally, we include strong consideration for the neural latencies, the Lyapunov stability, and the neural properties being reproduced by the model.     

Blindsight: spontaneous scanning of complex scenes

A new study of monkeys with blindsight has provided some surprising new insights into the visual properties that remain salient without a functioning primary visual cortex and may help improve rehabilitation strategies used with human hemianopes.     

Processing of complex stimuli and natural scenes in the visual cortex

A major part of vision research builds on the assumption that processing of visual stimuli can be understood on the basis of knowledge about the processing of simplified, artificial stimuli. Recent experimental advances, however, show that a combination of responses to simplified stimuli does not adequately describe responses to natural visual scenes. The systems performance exceeds the performance predicted from understanding its basic constituents. This highlights the fact that the visual system is specifically adapted to the properties of its everyday input and can only fully be understood when probed with naturalistic stimuli.     

Fibrin glue eliminates the need for packing after complex liver injuries.

Hemostasis after traumatic liver injury can be extremely difficult to obtain, particularly in coagulopathic patients who have suffered extensive liver damage. We determined the ability of a fibrin glue preparation (FG) to terminate ongoing bleeding using a new, clinically relevant porcine model of complex hepatic injury. Anesthetized swine (n = 6, 18 to 19 kg) received an external blast to the right upper abdomen and were immediately anticoagulated with intravenous heparin (200 u/kg). Uncontrolled hemorrhage from blast continued from time of injury (t = 0 minutes) to t = 15 minutes. Lactated Ringer's solution was infused to keep mean arterial pressure (MAP) > 80 mm Hg until the end of experiment (t = 90 minutes). Animals underwent routine surgical techniques to control bleeding, and FG was employed in the event these measures failed. Estimated blood loss and fluid resuscitation volume were measured. Serial MAP, arterial base excess, and temperature were recorded. Animals were severely injured with significant blood loss prior to laparotomy (26 +/- 6 cc/kg) and during routine surgical efforts to arrest hemorrhage (11 +/- 2 cc/kg). Bleeding could not be controlled with standard techniques in any animal. FG rapidly controlled hemorrhage and eliminated the need for packing. Re-bleeding was noted in only one animal (portal vein injury). FG can control severe hepatic hemorrhage when surgical techniques fail. Further work in the clinical arena is warranted to determine the potential benefits of FG in arresting hemorrhage in hemodynamically unstable coagulopathic patients with complex hepatic injuries.     

Processing of complex sounds in the auditory system

The coding of complex sounds in the early auditory system has a 'standard model' based on the known physiology of the cochlea and main brainstem pathways. This model accounts for a wide range of perceptual capabilities. It is generally accepted that high cortical areas encode abstract qualities such as spatial location or speech sound identity. Between the early and late auditory system, the role of primary auditory cortex (A1) is still debated. A1 is clearly much more than a 'whiteboard' of acoustic information-neurons in A1 have complex response properties, showing sensitivity to both low-level and high-level features of sounds.     

Influences of attention on auditory aftereffects following purely visual adaptation

Recently, Kitagawa and Ichihara (2002) demonstrated that visual adaptation to an expanding or contracting disk produces a cross-modal visually-induced auditory loudness aftereffect (VALAE), which they attributed to cross-correlations of motion in three-dimensional space. Our experiments extend their results by providing evidence that attending selectively to one of two competing visual stimuli of the same saliency produces a cross-modal VALAE that favors the attended stimulus. These cross-modal attentional effects suggest the existence of integrative spatial mechanisms between vision and audition that are affected by attention.     

Stimulus-driven orienting of visuo-spatial attention in complex dynamic environments

In everyday life attention operates within complex and dynamic environments, while laboratory paradigms typically employ simple and stereotyped stimuli. This fMRI study investigated stimulus-driven spatial attention using a virtual-environment video. We explored the influence of bottom-up signals by computing saliency maps of the environment and by introducing attention-grabbing events in the video. We parameterized the efficacy of these signals for the orienting of spatial attention by measuring eye movements and used these parameters to analyze the imaging data. The efficacy of bottom-up signals modulated ongoing activity in dorsal fronto-parietal regions and transient activation of the ventral attention system. Our results demonstrate that the combination of computational, behavioral, and imaging techniques enables studying cognitive functions in ecologically valid contexts. We highlight the central role of the efficacy of stimulus-driven signals in both dorsal and ventral attention systems, with a dissociation of the efficacy of background salience versus distinctive events in the two systems.     

Processing of complex auditory patterns in musicians and nonmusicians

In the present study we investigated the capacity of the memory store underlying the mismatch negativity (MMN) response in musicians and nonmusicians for complex tone patterns. While previous studies have focused either on the kind of information that can be encoded or on the decay of the memory trace over time, we studied capacity in terms of the length of tone sequences, i.e., the number of individual tones that can be fully encoded and maintained. By means of magnetoencephalography (MEG) we recorded MMN responses to deviant tones that could occur at any position of standard tone patterns composed of four, six or eight tones during passive, distracted listening. Whereas there was a reliable MMN response to deviant tones in the four-tone pattern in both musicians and nonmusicians, only some individuals showed MMN responses to the longer patterns. This finding of a reliable capacity of the short-term auditory store underlying the MMN response is in line with estimates of a three to five item capacity of the short-term memory trace from behavioural studies, although pitch and contour complexity covaried with sequence length, which might have led to an understatement of the reported capacity. Whereas there was a tendency for an enhancement of the pattern MMN in musicians compared to nonmusicians, a strong advantage for musicians could be shown in an accompanying behavioural task of detecting the deviants while attending to the stimuli for all pattern lengths, indicating that long-term musical training differentially affects the memory capacity of auditory short-term memory for complex tone patterns with and without attention. Also, a left-hemispheric lateralization of MMN responses in the six-tone pattern suggests that additional networks that help structuring the patterns in the temporal domain might be recruited for demanding auditory processing in the pitch domain.     

Brain networks of novelty-driven involuntary and cued voluntary auditory attention shifting

In everyday life, we need a capacity to flexibly shift attention between alternative sound sources. However, relatively little work has been done to elucidate the mechanisms of attention shifting in the auditory domain. Here, we used a mixed event-related/sparse-sampling fMRI approach to investigate this essential cognitive function. In each 10-sec trial, subjects were instructed to wait for an auditory "cue" signaling the location where a subsequent "target" sound was likely to be presented. The target was occasionally replaced by an unexpected "novel" sound in the uncued ear, to trigger involuntary attention shifting. To maximize the attention effects, cues, targets, and novels were embedded within dichotic 800-Hz vs. 1500-Hz pure-tone "standard" trains. The sound of clustered fMRI acquisition (starting at t?=?7.82 sec) served as a controlled trial-end signal. Our approach revealed notable activation differences between the conditions. Cued voluntary attention shifting activated the superior intra--parietal sulcus (IPS), whereas novelty-triggered involuntary orienting activated the inferior IPS and certain subareas of the precuneus. Clearly more widespread activations were observed during voluntary than involuntary orienting in the premotor cortex, including the frontal eye fields. Moreover, we found -evidence for a frontoinsular-cingular attentional control network, consisting of the anterior insula, inferior frontal cortex, and medial frontal cortices, which were activated during both target discrimination and voluntary attention shifting. Finally, novels and targets activated much wider areas of superior temporal auditory cortices than shifting cues.     

Some electrophysiological and hemodynamic characteristics of auditory selective attention in norm and schizophrenia

Six patients in the state of remission after the first episode ofjuvenile schizophrenia and seven sex- and age-matched mentally healthy subjects were examined by fMRI and ERP methods. The auditory oddball paradigm was applied. Differences in P300 parameters didn't reach the level of significance, however, a significantly higher hemodynamic response to target stimuli was found in patients bilaterally in the supramarginal gyrus and in the right medial frontal gyrus, which points to pathology of these brain areas in supporting of auditory selective attention.     

Selective attention and memory: evoked potentials in visual and auditory verbal competition

The brain mechanisms of the selective verbal attention were studied using evoked potential (EP) technique. It was shown that the late "cognitive" EP components (400-800 ms) related to memory function were more positive to the words presented via a relevant sensory channel and more negative to irrelevant words. The hypothesis is advanced that words delivered via two competing sensory channels, such as visual and auditory, are perceived, i.e., the subject sees and hears them. However, irrelevant signals are not stored in episodic memory due to the active inhibition of the information transmission to the hippocampal structures.     

EEG correlates of the states of visual and auditory attention in healthy subjects

In order to determine more accurately the EEG markers of different types of attention (AT) of a healthy adult, 14 young healthy subjects (aged 18–30 years) were subjected to spectral coherent analysis of the electrical activity of the brain in the baseline state and during activation of different forms of AT (the orienting response to the sound tone and opening of the eyes, involuntary and voluntary visual AT). In the last two cases, specially developed computer-aided techniques were used. The quantitative differences in the states were assessed on the basis of nonparametric (the Mann-Whitney test) and parametric (Student’s t test) statistics. In three subjects, EEG and fMRI comparisons of the brain response to opening of the eyes were made. It was shown that the activation of different forms of AT in healthy subjects is accompanied by considerable diffuse nonspecific changes in the EEG spectral coherent characteristics (a decrease in the average spectral frequency and power, as well as in coherence) in combination with more local, more often oppositely directed shifts in the region of the cortical representation of the working analyzer. Complex systemic rearrangements of the brain activity involving all components of the activating system, as well as the specifics of different forms of AT connected with the rearrangement of activity between its divisions, are reflected in the diffuse changes of intercentral interaction. For example, marked reactivity of the symmetrical frontopolar (F _p1-F _p2) and the anterotemporal (F ₇-F ₈) cortical areas with unidirectional maximum shifts during voluntary AT is likely to reflect the responses of the frontothalamic component of the activating system. The reciprocity of the behavior of interhemispheric frontopolar and temporal relationships seems to be determined by the activity of its different components: frontothalamic and hippocampal. The local component of the EEG response to opening of the eyes in the form of increased α coherence in the occipital areas is coupled with increased oxygenation of blood in the cortical representation of the visual analyzer (the +BOLD effect of the fMRI response).     

Electric imaging through active electrolocation: implication for the analysis of complex scenes

The electric sense of mormyrids is often regarded as an adaptation to conditions unfavourable for vision and in these fish it has become the dominant sense for active orientation and communication tasks. With this sense, fish can detect and distinguish the electrical properties of the close environment, measure distance, perceive the 3-D shape of objects and discriminate objects according to distance or size and shape, irrespective of conductivity, thus showing a degree of abstraction regarding the interpretation of sensory stimuli. The physical properties of images projected on the sensory surface by the fish's own discharge reveal a "Mexican hat" opposing centre-surround profile. It is likely that computation of the image amplitude to slope ratio is used to measure distance, while peak width and slope give measures of shape and contrast. Modelling has been used to explore how the images of multiple objects superimpose in a complex manner. While electric images are by nature distributed, or 'blurred', behavioural strategies orienting sensory surfaces and the neural architecture of sensory processing networks both contribute to resolving potential ambiguities. Rostral amplification is produced by current funnelling in the head and chin appendage regions, where high density electroreceptor distributions constitute foveal regions. Central magnification of electroreceptive pathways from these regions particularly favours the detection of capacitive properties intrinsic to potential living prey. Swimming movements alter the amplitude and contrast of pre-receptor object-images but image modulation is normalised by central gain-control mechanisms that maintain excitatory and inhibitory balance, removing the contrast-ambiguity introduced by self-motion in much the same way that contrast gain-control is achieved in vision.     

Successful implementation of cooperative handling eliminates the need for restraint in a complex non-human primate disease model

Background Streptozotocin‐induced diabetic non‐human primates are used to study efficacy and safety of innovative immunosuppression after islet transplantation. We implemented a training program for medical management of a chronic disease state. Methods Cooperation with hand feeding and drinking, shifting, and limb presentation were trained utilizing predominately positive but also negative reinforcement in 52 animals compared with 28 macaques subjected to conventional physical and/or chemical restraint. The success and timing of behavior acquisition was evaluated in a representative subset of 14 animals. Results Over 90% of animals were successful in behavior acquisition. Programmatically this resulted in complete elimination of chair restraint and negligible requirement for sedation. About half of the trained animals had no‐to‐moderate thymic involution, indicative of a substantial reduction in stress. Conclusion Cooperative handling enhances animal well‐being. This contributes to validity of scientific results and eliminates model‐induced confounding that can obstruct interpretation of safety and efficacy data.