Investigating saccade programming in the praying mantis Tenodera aridifolia using distracter interference paradigms

To investigate the saccadic system in the mantis, I applied distracter interference paradigms. These involved presenting the mantis with a fixation target and one or several distracters supposed to affect saccades towards the target. When a single target was presented, a medium-sized target located in its lower visual field elicited higher rates of saccade response. This preference for target size and position was also observed when a target and a distracter were presented simultaneously. That is, the mantis chose and fixated the target rather than a distracter that was much smaller or larger than the target, or was located above the target. Furthermore, the mantis' preference was not affected by increasing the number of distracters. However, the presence of the distracter decreased the occurrence rate of saccade and increased the response time to saccade. I conclude that distracter interference paradigms are an effective way of investigating the visual processing underlying saccade generation in the mantis. Possible mechanisms of saccade generation in the mantis are discussed.     

Spatial interactions in rapid pattern discrimination

We measured reaction times (RTs) for identification of a target among distracters under stabilized image conditions in which the positions of the target and the distracters were constant within a single experimental session. Under these conditions, the observer need not search for the target because its position is known. We nevertheless found that the presence of even a single distracter could elevate RTs. The magnitude of this effect depended on the distance of the distracter from the target and, for some observers, the distance of the distracter from the fovea. When we added not one but six background elements in a ring around the target, RT increased even more. If, apart from these neighboring distracters, the target was surrounded by more distracters located beyond the nearest neighbors, RT was, in general, not increased further. These findings suggest that adding background elements in a search task can elevate RTs in ways that are not dependent on the positional uncertainty of the target.     

Exploring BOLD Changes during Spatial Attention in Non-Stimulated Visual Cortex

Blood oxygen level-dependent (BOLD) responses were measured in parts of primary visual cortex that represented unstimulated visual field regions at different distances from a stimulated central target location. The composition of the visual scene varied by the presence or absence of additional peripheral distracter stimuli. Bottom-up effects were assessed by comparing peripheral activity during central stimulation vs. no stimulation. Top-down effects were assessed by comparing active vs. passive conditions. In passive conditions subjects simply watched the central letter stimuli and in active conditions they had to report occurrence of pre-defined targets in a rapid serial letter stream. Onset of the central letter stream enhanced activity in V1 representations of the stimulated region. Within representations of the periphery activation decreased and finally turned into deactivation with increasing distance from the stimulated location. This pattern was most pronounced in the active conditions and during the presence of peripheral stimuli. Active search for a target did not lead to additional enhancement at areas representing the attentional focus but to a stronger deactivation in the vicinity. Suppressed neuronal activity was also found in the non distracter condition suggesting a top-down attention driven effect. Our observations suggest that BOLD signal decreases in primary visual cortex are modulated by bottom-up sensory-driven factors such as the presence of distracters in the visual field as well as by top-down attentional processes.     

Transfer of a Serial Representation between Two Distinct Tasks by Rhesus Macaques

Do animals form task-specific representations, or do those representations take a general form that can be applied to qualitatively different tasks? Rhesus monkeys (Macaca mulatta) learned the ordering of stimulus lists using two different serial tasks, in order to test whether prior experience in each task could be transfered to the other, enhancing performance. The simultaneous chaining paradigm delivered rewards only after subjects responded in the correct order to all stimuli displayed on a touch sensitive video monitor. The transitive inference paradigm presented pairs of items and delivered rewards when subjects selected the item with the lower ordinal rank. After learning a list in one paradigm, subjects’ knowledge of that list was tested using the other paradigm. Performance was enhanced from the very start of transfer training. Transitive inference performance was characterized by ‘symbolic distance effects,’ whereby the ordinal distance between stimuli in the implied list ordering was strongly predictive of the probability of a correct response. The patterns of error displayed by subjects in both tasks were best explained by a spatially coded representation of list items, regardless of which task was used to learn the list. Our analysis permits properties of this representation to be investigated without the confound of verbal reasoning.     

Central representation of spatial and temporal surface wave parameters in the African clawed frog

Xenopus laevis employs mechano-sensory lateral lines to, for instance, capture arthropods on the surface of turbid waters with poor visibility based on incoming wave signals. To characterise central representations of surface waves emitted from different locations, responses to several wave parameters were extracellularly recorded across brainstem, midbrain and thalamic areas. Overall, 339 of 411 statistically analysed responses showed significantly altered spike rates during the presentation of surface waves. Of these units, 45.1?% were obtained in the torus semicircularis including its laminar subnucleus (23.3?%) that is known to process auditory cues. Wave parameters contributing to central object representations were indicated by response rates that systematically varied with amplitude (76.3?% of 160 tested units), frequency (74.4?% of 270 tested units), source angle (93.7?% of 79 tested units), or source distance (63.8?% of 218 tested units). Map-like parameter representations were rather diffuse, yet an increased fraction of units tuned to frontal source angles was observed at deeper tissue layers (>180?μm), and an increased fraction of best neuronal responses to low wave frequencies (≤25?Hz) at rostral midbrain sections. Responses to wave frequencies remained largely robust across tested unit samples independent of source angles, and distances (N?=?62). In comparison, spatial response characteristics seemed fragile across different wave frequencies in 68.3?% of 41 recordings.     

Electrophysiological evidence for immature processing capacity and filtering in visuospatial working memory in adolescents

The present study investigated the development of visuospatial working memory (VSWM) capacity and the efficiency of filtering in VSWM in adolescence. To this end, a group of IQ-matched adults and adolescents performed a VSWM change detection task with manipulations of WM-load and distraction, while performance and electrophysiological contralateral delay activity (CDA) were measured. The CDA is a lateralized ERP marker of the number of targets and distracters that are selectively encoded/maintained in WM from one hemifield of the memory display. Significantly lower VSWM-capacity (Cowan's K) was found in adolescents than adults, and adolescents' WM performance (in terms of accuracy and speed) also suffered more from the presence of distracters. Distracter-related CDA responses were partly indicative of higher distracter encoding/maintenance in WM in adolescents and were positively correlated with performance measures of distracter interference. This correlation suggests that the higher interference of distracters on WM performance in adolescents was caused by an inability to block distracters from processing and maintenance in WM. The lower visuospatial WM-capacity (K) in adolescents in the high load (3 items) condition was accompanied by a trend (p<.10) towards higher CDA amplitudes in adolescents than adults, whereas CDA amplitudes in the low load (1 item) condition were comparable between adolescents and adults. These findings point to immaturity of frontal-parietal WM-attention networks that support visuospatial WM processing in adolescence.     

Ultra scaledown to predict filtering centrifugation of secreted antibody fragments from fungal broth

Extracellularly expressed anti-hen egg lysozyme single-chain antibody fragments (scFv) produced by Aspergillus awamori were recovered using filtering centrifugation. Two filtering centrifuges with 0.5- and 30-L capacities were used to represent laboratory- and pilot-scale equipment, respectively. Critical regime analysis using the computational fluid dynamics (CFD) technique provided information about the local energy dissipation rates in both units. Experimental data indicated loss of scFv activity for energy dissipation rates above about 2.0 x 10(4) W kg(-1). This loss of activity increased in the presence of gas-liquid interfaces during filtering centrifugation. An ultra scaledown filtering centrifuge with a maximum working volume of 35 mL was designed to mimic the operating conditions identified by the critical regime analysis for the laboratory- and pilot-plant-scale units. The recovered scFv activity levels and the separation performance of the three units were comparable when operated at equal maximum energy dissipation rates.     

Fine-Grained,Local Maps and Coarse,Global Representations Support Human Spatial Working Memory

While sensory processes are tuned to particular features, such as an object''s specific location, color or orientation, visual working memory (vWM) is assumed to store information using representations, which generalize over a feature dimension. Additionally, current vWM models presume that different features or objects are stored independently. On the other hand, configurational effects, when observed, are supposed to mainly reflect encoding strategies. We show that the location of the target, relative to the display center and boundaries, and overall memory load influenced recall precision, indicating that, like sensory processes, capacity limited vWM resources are spatially tuned. When recalling one of three memory items the target distance from the display center was overestimated, similar to the error when only one item was memorized, but its distance from the memory items'' average position was underestimated, showing that not only individual memory items'' position, but also the global configuration of the memory array may be stored. Finally, presenting the non-target items at recall, consequently providing landmarks and configurational information, improved precision and accuracy of target recall. Similarly, when the non-target items were translated at recall, relative to their position in the initial display, a parallel displacement of the recalled target was observed. These findings suggest that fine-grained spatial information in vWM is represented in local maps whose resolution varies with distance from landmarks, such as the display center, while coarse representations are used to store the memory array configuration. Both these representations are updated at the time of recall.     

Menstrual cycle shifts in attentional bias for courtship language

The current study investigated whether women show an attentional bias toward courtship language during the fertile phase of their menstrual cycle. Thirty heterosexual women (17 naturally cycling, 13 using hormonal contraceptives) completed a dichotic listening task on both a high and low fertility day of their menstrual cycle. Participants were asked to verbally repeat (shadow) an emotionally neutral target passage played in one ear while either a neutral or courtship distracter was played in the other ear. Courtship distracters were flirtatious in content but not overtly sexual. Shadowing errors were coded as a measure of attentional bias toward the distracter. Saliva samples were taken to determine whether levels of estradiol, progesterone and/or testosterone correlated with task performance. As predicted, naturally cycling women made more shadowing errors when listening to a courtship distracter during the fertile phase of their cycle than during the nonfertile phase. This effect was moderated by relationship status, such that fertile, mated women showed an attentional bias for courtship language but fertile single women did not. However, because of small sample sizes in the analysis, this relationship should be viewed as preliminary. Hormonal analysis revealed that higher levels of salivary estradiol predicted greater attentional bias toward courtship language in naturally cycling women. These results suggest that women's attention is drawn to verbal courtship signals when they are fertile, and that this shift is linked to increased estradiol release during the periovulatory phase.     

Growth-rate dependent feeding rates in Daphnia pulicaria and Brachionus rubens: adaptation to intermediate time-scale variations in food abundance

The hypothesis was tested that zooplankton can adapt to fluctuationsof their food resources at intermediate time scales in orderto maximize their energy input. The cladoceran Daphnia pulicariaand the rotifer Brachionus rubens were cultured at a range offixed growth rates and then offered radioactively labelled algaeat limiting and non-limiting concentrations to determine theirfunctional response. Rotifers and cladocerans showed a remarkablysimilar response. Animals growing at low growth rates had highermaximum filtering rates, i.e. were better adapted to low foodconcentrations than those growing at high rates. The growthrate did not affect the maximum ingestion rate in any of thespecies, thus indicating that adaptation to the prevailing foodconditions was based on the process of food collection. Bothspecies were heavier when cultured at high growth rates. Plottingthe weight-specific maximum filtering rate versus the growthrate resulted in a pronounced negative slope. The slope forthe weight-specific maximum ingestion rate was also negative.Hence filtering and ingestion rates seem to be determined bythe size of the zooplankton, not by their weight.     

Structure of Spike Count Correlations Reveals Functional Interactions between Neurons in Dorsolateral Prefrontal Cortex Area 8a of Behaving Primates

Neurons within the primate dorsolateral prefrontal cortex (dlPFC) are clustered in microcolumns according to their visuospatial tuning. One issue that remains poorly investigated is how this anatomical arrangement influences functional interactions between neurons during behavior. To investigate this question we implanted 4 mm×4 mm multielectrode arrays in two macaques'' dlPFC area 8a and measured spike count correlations (r_sc) between responses of simultaneously recorded neurons when animals maintained stationary gaze. Positive and negative r_sc were significantly higher than predicted by chance across a wide range of inter-neuron distances (from 0.4 to 4 mm). Positive r_sc were stronger between neurons with receptive fields (RFs) separated by ≤90° of angular distance and progressively decreased as a function of inter-neuron physical distance. Negative r_sc were stronger between neurons with RFs separated by >90° and increased as a function of inter-neuron distance. Our results show that short- and long-range functional interactions between dlPFC neurons depend on the physical distance between them and the relationship between their visuospatial tuning preferences. Neurons with similar visuospatial tuning show positive r_sc that decay with inter-neuron distance, suggestive of excitatory interactions within and between adjacent microcolumns. Neurons with dissimilar tuning from spatially segregated microcolumns show negative r_sc that increase with inter-neuron distance, suggestive of inhibitory interactions. This pattern of results shows that functional interactions between prefrontal neurons closely follow the pattern of connectivity reported in anatomical studies. Such interactions may be important for the role of the prefrontal cortex in the allocation of attention to targets in the presence of competing distracters.     

Postdictive modulation of visual orientation

The present study investigated how visual orientation is modulated by subsequent orientation inputs. Observers were presented a near-vertical Gabor patch as a target, followed by a left- or right-tilted second Gabor patch as a distracter in the spatial vicinity of the target. The task of the observers was to judge whether the target was right- or left-tilted (Experiment 1) or whether the target was vertical or not (Supplementary experiment). The judgment was biased toward the orientation of the distracter (the postdictive modulation of visual orientation). The judgment bias peaked when the target and distracter were temporally separated by 100 ms, indicating a specific temporal mechanism for this phenomenon. However, when the visibility of the distracter was reduced via backward masking, the judgment bias disappeared. On the other hand, the low-visibility distracter could still cause a simultaneous orientation contrast, indicating that the distracter orientation is still processed in the visual system (Experiment 2). Our results suggest that the postdictive modulation of visual orientation stems from spatiotemporal integration of visual orientation on the basis of a slow feature matching process.     

The effect of visual cues on difficulty ratings for segregation of musical streams in listeners with impaired hearing

Background

Enjoyment of music is an important part of life that may be degraded for people with hearing impairments, especially those using cochlear implants. The ability to follow separate lines of melody is an important factor in music appreciation. This ability relies on effective auditory streaming, which is much reduced in people with hearing impairment, contributing to difficulties in music appreciation. The aim of this study was to assess whether visual cues could reduce the subjective difficulty of segregating a melody from interleaved background notes in normally hearing listeners, those using hearing aids, and those using cochlear implants.

Methodology/Principal Findings

Normally hearing listeners (N = 20), hearing aid users (N = 10), and cochlear implant users (N = 11) were asked to rate the difficulty of segregating a repeating four-note melody from random interleaved distracter notes. The pitch of the background notes was gradually increased or decreased throughout blocks, providing a range of difficulty from easy (with a large pitch separation between melody and distracter) to impossible (with the melody and distracter completely overlapping). Visual cues were provided on half the blocks, and difficulty ratings for blocks with and without visual cues were compared between groups. Visual cues reduced the subjective difficulty of extracting the melody from the distracter notes for normally hearing listeners and cochlear implant users, but not hearing aid users.

Conclusion/Significance

Simple visual cues may improve the ability of cochlear implant users to segregate lines of music, thus potentially increasing their enjoyment of music. More research is needed to determine what type of acoustic cues to encode visually in order to optimise the benefits they may provide.     

Comparison of methods for estimating motor unit firing rate time series from firing times

The central nervous system regulates recruitment and firing of motor units to modulate muscle tension. Estimation of the firing rate time series is typically performed by decomposing the electromyogram (EMG) into its constituent firing times, then lowpass filtering a constituent train of impulses. Little research has examined the performance of different estimation methods, particularly in the inevitable presence of decomposition errors. The study of electrocardiogram (ECG) and electroneurogram (ENG) firing rate time series presents a similar problem, and has applied novel simulation models and firing rate estimators. Herein, we adapted an ENG/ECG simulation model to generate realistic EMG firing times derived from known rates, and assessed various firing rate time series estimation methods. ENG/ECG-inspired rate estimation worked exceptionally well when EMG decomposition errors were absent, but degraded unacceptably with decomposition error rates of ⩾1%. Typical EMG decomposition error rates—even after expert manual review—are 3–5%. At realistic decomposition error rates, more traditional EMG smoothing approaches performed best, when optimal smoothing window durations were selected. This optimal window was often longer than the 400 ms duration that is commonly used in the literature. The optimal duration decreased as the modulation frequency of firing rate increased, average firing rate increased and decomposition errors decreased. Examples of these rate estimation methods on physiologic data are also provided, demonstrating their influence on measures computed from the firing rate estimate.     

Neuronal ensemble dynamics in associative learning

Associative learning restructures the activity of numerous neurons distributed across cortical and subcortical regions. Individual neurons change the rate or timing of spiking patterns in response to environmental stimuli as they become associated with salient outcomes. Recent large–scale activity monitoring in rodents has uncovered that these learning-related changes occur concertedly across groups of neurons within and between brain regions. These changes yield neuronal representations of learned associations in three types of ensemble dynamics: ensemble firing rates, multineuron coactivity, and sequential activity. Here, I review some of the most robust demonstrations of these dynamics in the rodent neocortex and hippocampus and discuss their potential function in memory encoding, consolidation, and retrieval.     

Relative motion parallax and target localisation in the locust,Schistocerca gregaria

Summary This paper addresses two questions. 1. Does Schistocerca gregaria detect edges which are defined solely by velocity-contrast, that is by the difference in the image speeds generated by an object and its background when the locust moves? 2. Is the locust's ability to measure the distance of a target by motion parallax independent of the relative motion between target and back-ground?A locust walking on a circular platform was surrounded by a stationary cylinder which was lined with an irregular texture. Against this background, the insect viewed 3 stationary, equidistant targets. One target was black, one grey and the last was textured like the cylinder. Peers and jumps were aimed preferentially at the textured and black targets showing that targets can be detected by virtue of their velocity-contrast with the background. When textured targets were wide, jumps were seen to be aimed at the targets' edge.To assess whether velocity-contrast between target and background distorts distance-estimates, we used jump-velocity as a measure of apparent distance and examined how it varied with different arrangements of target and background. When a textured background is close to a target or the target is very wide, velocity contrast is small. The locust's jump-velocity is then 10% greater than when velocity-contrast is increased by making the background distant or the target narrow. This suggests that the locust is efficient at separating signals encoding absolute motion from those encoding relative motion.     

Controlling attention to nociceptive stimuli with working memory

Background

Because pain often signals the occurrence of potential tissue damage, a nociceptive stimulus has the capacity to involuntarily capture attention and take priority over other sensory inputs. Whether distraction by nociception actually occurs may depend upon the cognitive characteristics of the ongoing activities. The present study tested the role of working memory in controlling the attentional capture by nociception.

Methodology and Principal Findings

Participants performed visual discrimination and matching tasks in which visual targets were shortly preceded by a tactile distracter. The two tasks were chosen because of the different effects the involvement of working memory produces on performance, in order to dissociate the specific role of working memory in the control of attention from the effect of general resource demands. Occasionally (i.e. 17% of the trials), tactile distracters were replaced by a novel nociceptive stimulus in order to distract participants from the visual tasks. Indeed, in the control conditions (no working memory), reaction times to visual targets were increased when the target was preceded by a novel nociceptive distracter as compared to the target preceded by a frequent tactile distracter, suggesting attentional capture by the novel nociceptive stimulus. However, when the task required an active rehearsal of the visual target in working memory, the novel nociceptive stimulus no longer induced a lengthening of reaction times to visual targets, indicating a reduction of the distraction produced by the novel nociceptive stimulus. This effect was independent of the overall task demands.

Conclusion and Significance

Loading working memory with pain-unrelated information may reduce the ability of nociceptive input to involuntarily capture attention, and shields cognitive processing from nociceptive distraction. An efficient control of attention over pain is best guaranteed by the ability to maintain active goal priorities during achievement of cognitive activities and to keep pain-related information out of task settings.     

Electrolocation in the presence of jamming signals: behavior

Electrolocation behavior of Apteronotus leptorhynchus was studied by monitoring the animal's ability to maintain orientation to a variety of moving electrolocation targets. The primary goal of this study was to determine the relative effectiveness of various types of electrical 'jamming signals' in disrupting electrolocation performance. 1. Two measures of electrolocation performance were used: The latency between the electrolocation target motion and the fish's following response, and the minimum distance separating the fish from the target during the target movement sequence. Latency increased and minimum fish-target distance decreased as target size was decreased, and when large diameter ceramic targets were used as control stimuli the fish were less able to avoid, and frequently collided with, these 'electrically transparent' objects. 2. Four types of jamming signals were used in attempts to mask the electrosensory input used for electrolocation. Broad-band noise and sinusoidal signals, different in frequency by a few Hz from the animal's personal electric organ discharge (DF stimuli), were used to jam the tuberous electroreceptors. Five Hz and 50 Hz sinusoidal signals were used to jam the low-frequency or ampullary receptor system. Both the noise and the DF stimuli were effective in reducing electrolocation performance, and the threshold intensity for behavior deterioration was about three-fold lower for DF stimuli as compared to the noise. The rate of change of response deterioration as a function of increasing jamming intensity was, however, not different for these two types of stimuli. Neither the 50 Hz nor the 5 Hz jamming signals caused electrolocation deterioration when presented alone. However, 5 Hz jamming, when added to either the noise or DF jamming, did result in significant increments in response deterioration. This suggests that the ampullary receptors can provide supplementary information for electrolocation. 3. Electrolocation performance deterioration was also studied with various difference frequencies between an animal's EOD and the sinusoidal jamming stimulus. Increasing DF results in decreased electrolocation deterioration, but even at the highest DF frequencies used (128 Hz) significant response degradation was observed. 4. The apparent differences in the effectiveness of noise and DF stimulation in reducing electrolocation performance are largely accounted for by the differential effects of the tuberous electroreceptor filter characteristics on these two types of signals.     

Transient attention enhances perceptual performance and FMRI response in human visual cortex

When a visual stimulus suddenly appears, it captures attention, producing a transient improvement of performance on basic visual tasks. We investigate the effect of transient attention on stimulus representations in early visual areas using rapid event-related fMRI. Participants discriminated the orientation of one of two gratings preceded or followed by a nonpredictive peripheral cue. Compared to control conditions, precueing the target location improved performance and produced a larger fMRI response in corresponding retinotopic areas. This enhancement progressively increased from striate to extrastriate areas. Control conditions indicated that the enhanced fMRI response was not due to sensory summation of cue and target signals. Thus, an uninformative precue increases both perceptual performance and the concomitant stimulus-evoked activity in early visual areas. These results provide evidence regarding the retinotopically specific neural correlate for the effects of transient attention on early vision.