Nesting in close quarters: Causes and benefits of high-density nesting behaviour in Painted Turtles

Many oviparous reptiles nest in aggregations and with temporal synchrony. We hypothesized that these traits reflect attraction by conspecifics rather than limiting suitable habitat. We quantified whether Painted Turtles (Chrysemys picta (Schneider, 1783)) in Algonquin Park, Ontario, were nesting communally, identified cues females used to select nest sites, and tested whether hatching success was higher in spatially-clustered nests. We found that nests were closer to one another than expected by chance (i.e., were clustered), but that individual nest site selection was only weakly influenced by micro-habitat characteristics. Survival of clustered nests (49%) was not significantly higher than that of solitary nests (39%). When turtle models were placed on the nesting embankment, females nested most often with the highest density of models. Given that reproductive lifespan is the major axis of fitness and that there was little benefit to nest survival in clustered nests, we suggest that clustering is related to females cueing to conspecific nests to expedite the nesting process and gain a good-quality nest site (chosen by the first nesting female in the cluster) while investing little energy in nest-site selection. This strategy may reduce time spent on land, thereby minimizing chances of dehydration, temperature stress, and adult depredation.

How synaptic strength, short-term plasticity, and temporal factors contribute to neuronal spike output

To compute spiking responses, neurons integrate inputs from thousands of synapses whose strengths span an order of magnitude. Intriguingly, in mouse neocortex, the small minority of 'strong' synapses is found predominantly between similarly tuned cells, suggesting they are the synapses that determine a neuron's spike output. This raises the question of how other computational primitives, such as 'background' activity from the majority of synapses, which are 'weak', short-term plasticity, and temporal synchrony contribute to spiking. First, we combined extracellular stimulation and whole-cell recordings in mouse barrel cortex to map the distribution of excitatory postsynaptic potential (EPSP) amplitudes and paired-pulse ratios of excitatory synaptic connections converging onto individual layer 2/3 (L2/3) neurons. While generally net short-term plasticity was weak, connections with EPSPs > 2 mV displayed pronounced paired-pulse depression. EPSP amplitudes and paired-pulse ratios of connections converging onto the same neurons spanned the full range observed across L2/3 and there was no indication that strong synapses nor those with particular short-term plasticity properties were associated with particular cells, which critically constrains theoretical models of cortical filtering. To investigate how different computational primitives of synaptic information processing interact to shape spiking, we developed a computational model of a pyramidal neuron in the rodent L2/3 circuitry: firing rates and pairwise correlations of presynaptic inputs were constrained by in vivo observations, while synaptic strength and short-term plasticity were set based on our experimental data. Importantly, we found that the ability of strong inputs to evoke spiking critically depended on their high temporal synchrony and high firing rates observed in vivo and on synaptic background activity - and not primarily on synaptic strength, which in turn further enhanced information transfer. Depression of strong synapses was critical for maintaining a neuron's responsivity and prevented runaway excitation. Our results provide a holistic framework of how cortical neurons exploit complex synergies between temporal coding, synaptic properties, and noise in order to transform synaptic inputs into output firing.

Visual field differences in temporal synchrony processing for audio-visual stimuli

Audio-visual integration relies on temporal synchrony between visual and auditory inputs. However, differences in traveling and transmitting speeds between visual and auditory stimuli exist; therefore, audio-visual synchrony perception exhibits flexible functions. The processing speed of visual stimuli affects the perception of audio-visual synchrony. The present study examined the effects of visual fields, in which visual stimuli are presented, for the processing of audio-visual temporal synchrony. The point of subjective simultaneity, the temporal binding window, and the rapid recalibration effect were measured using temporal order judgment, simultaneity judgment, and stream/bounce perception, because different mechanisms of temporal processing have been suggested among these three paradigms. The results indicate that auditory stimuli should be presented earlier for visual stimuli in the central visual field than in the peripheral visual field condition in order to perceive subjective simultaneity in the temporal order judgment task conducted in this study. Meanwhile, the subjective simultaneity bandwidth was broader in the central visual field than in the peripheral visual field during the simultaneity judgment task. In the stream/bounce perception task, neither the point of subjective simultaneity nor the temporal binding window differed between the two types of visual fields. Moreover, rapid recalibration occurred in both visual fields during the simultaneity judgment tasks. However, during the temporal order judgment task and stream/bounce perception, rapid recalibration occurred only in the central visual field. These results suggest that differences in visual processing speed based on the visual field modulate the temporal processing of audio-visual stimuli. Furthermore, these three tasks, temporal order judgment, simultaneity judgment, and stream/bounce perception, each have distinct functional characteristics for audio-visual synchrony perception. Future studies are necessary to confirm the effects of compensation regarding differences in the temporal resolution of the visual field in later cortical visual pathways on visual field differences in audio-visual temporal synchrony.

Temporal Synchrony in Autism: a Systematic Review

Temporal synchrony is the alignment of processes in time within or across individuals in social interaction and is observed and studied in various domains using wide-ranging paradigms. Evidence suggesting reduced temporal synchrony in autism (e.g. compared to neurotypicals) has hitherto not been reviewed. To systematically review the magnitude and generalisability of the difference across different tasks and contexts, EBSCO, OVID, Web of Science, and Scopus databases were searched. Thirty-two studies were identified that met our inclusion criteria in audio-visual, audio-motor, visuo-tactile, visuo-motor, social motor, and conversational synchrony domains. Additionally, two intervention studies were included. The findings suggest that autistic participants showed reduced synchrony tendencies in every category of temporal synchrony reviewed. Implications, methodological weaknesses, and evidence gaps are discussed.

Negative impacts from latency masked by noise in simulated beamforming

Those experiencing hearing loss face severe challenges in perceiving speech in noisy situations such as a busy restaurant or cafe. There are many factors contributing to this deficit including decreased audibility, reduced frequency resolution, and decline in temporal synchrony across the auditory system. Some hearing assistive devices implement beamforming in which multiple microphones are used in combination to attenuate surrounding noise while the target speaker is left unattenuated. In increasingly challenging auditory environments, more complex beamforming algorithms are required, which increases the processing time needed to provide a useful signal-to-noise ratio of the target speech. This study investigated whether the benefits from signal enhancement from beamforming are outweighed by the negative impacts on perception from an increase in latency between the direct acoustic signal and the digitally enhanced signal. The hypothesis for this study is that an increase in latency between the two identical speech signals would decrease intelligibility of the speech signal. Using 3 gain / latency pairs from a beamforming simulation previously completed in lab, perceptual thresholds of SNR from a simulated use case were obtained from normal hearing participants. No significant differences were detected between the 3 conditions. When presented with 2 copies of the same speech signal presented at varying gain / latency pairs in a noisy environment, any negative intelligibility effects from latency are masked by the noise. These results allow for more lenient restrictions for limiting processing delays in hearing assistive devices.

Temporal Synchrony in Autism: A Systematic Review

A large number of studies have reported that autistic individuals show differences in their performance on temporal asynchrony tasks as compared to neurotypical individuals. Specifically, autistic individuals appear to show a reduced tendency towards synchrony. However, the evidence has hitherto not been reviewed in a systematic way, making it difficult to be sure of the magnitude and generalisability of the difference across different tasks and contexts. The present review aimed to systematically collect and synthesise the data on various types of temporal synchrony in autism across all ages in order to address this gap. A systematic search of the EBSCO, OVID, Web of Science, and Scopus databases was conducted, and the search strategies involved keywords and synonyms for “autism”, “temporal” and “synchrony”. Thirty-two studies were identified that met our inclusion criteria: 13 in the domain of audio-visual; three in audio-motor; three in visuo-tactile; three in visuo-motor; three in social motor; and five in conversational synchrony. An additional two studies focused on adapting an intervention method to improve interpersonal temporal synchrony in autistic individuals. The findings suggest that autistic participants showed reduced synchrony tendencies in every category of temporal synchrony that was reviewed. The findings are discussed in relation to existing knowledge of temporal processing and integration differences in autism. Limitations, future directions and potential clinical implications are also discussed.