Time perception: brain time or event time?

Recent experiments show that synchronous events can appear to an observer to occur at different times. Neural processing time delays are offered as an explanation of these temporal illusions, but equating perceived time with processing time leads to some thorny philosophical problems.     

Indian time for nature? A multi-level approach to American Indian outdoor time in everyday life

Social scientists have utilized daily time use studies as one method of understanding everyday lives. The bulk of this research, usually quantitative, identifies broad racial, ethnic and gender differences. Yet, certain groups and questions are typically excluded in daily time use research. One such group is American Indians. To address this lacuna, we look at the deeply discussed view that American Indians are closer to nature than other US ethnic groups. We use a nationally representative sample of individual daily time use (American Time Use Survey; n?=?136,960) to look at leisure time outdoors. Our results show that American Indians report greater time spent outdoors but that this is only statistically significant for those who identify as exclusively American Indian (not for American Indians that are multi- and bi-racial). This study confirms previous qualitative research that suggests American Indians have a distinct relationship with nature.     

How visual stimulus effects the time perception? The evidence from time perception of emotional videos

Time perception is defined as a subjective judgment on the elapsed time of an event. It can change according to both external and internal factors. There are two main paradigms of time perception; retrospective time perception (RTP) and prospective time perception (PTP). Two paradigms differ from each other according to whether the subject has knowledge on the importance of passage of time in the given task. Since RTP paradigm studies are harder to conduct, studies on RTP paradigm is far fewer than studies on PTP. Thus in the current study, both RTP and PTP paradigms are investigated. Also, time perception is discussed in relation to internal clock model and cognitive load. Emotional motion videos are used to create cognitive load and manipulate internal clock. Results showed the effect of emotion on time perception. Another major finding is that shorter videos are perceived longer whereas longer videos are perceived shorter as in accordance with Vierordt’s Law. However, there was no difference between RTP and PTP paradigms. These results indicate that emotional videos change our internal clock while a number of changes in a motion video create cognitive load causing disturbance of time perception.     

Are time delays always destabilizing? Revisiting the role of time delays and the Allee effect

One of the main challenges in ecology is to determine the cause of population fluctuations. Both theoretical and empirical studies suggest that delayed density dependence instigates cyclic behavior in many populations; however, underlying mechanisms through which this occurs are often difficult to determine and may vary within species. In this paper, we consider single species population dynamics affected by the Allee effect coupled with discrete time delay. We use two different mathematical formulations of the Allee effect and analyze (both analytically and numerically) the role of time delay in different feedback mechanisms such as competition and cooperation. The bifurcation value of the delay (that results in the Hopf bifurcation) as a function of the strength of the Allee effect is obtained analytically. Interestingly, depending on the chosen delayed mechanism, even a large time delay may not necessarily lead to instability. We also show that, in case the time delay affects positive feedback (such as cooperation), the population dynamics can lead to self-organized formation of intermediate quasi-stationary states. Finally, we discuss ecological implications of our findings.     

Dynamics from a time series: can we extract the phase resetting curve from a time series?

Recordings of the membrane potential from a bursting neuron were used to reconstruct the phase curve for that neuron for a limited set of perturbations. These perturbations were inhibitory synaptic conductance pulses able to shift the membrane potential below the most hyperpolarized level attained in the free running mode. The extraction of the phase resetting curve from such a one-dimensional time series requires reconstruction of the periodic activity in the form of a limit cycle attractor. Resetting was found to have two components. In the first component, if the pulse was applied during a burst, the burst was truncated, and the time until the next burst was shortened in a manner predicted by movement normal to the limit cycle. By movement normal to the limit cycle, we mean a switch between two well-defined solution branches of a relaxation-like oscillator in a hysteretic manner enabled by the existence of a singular dominant slow process (variable). In the second component, the onset of the burst was delayed until the end of the hyperpolarizing pulse. Thus, for the pulse amplitudes we studied, resetting was independent of amplitude but increased linearly with pulse duration. The predicted and the experimental phase resetting curves for a pyloric dilator neuron show satisfactory agreement. The method was applied to only one pulse per cycle, but our results suggest it could easily be generalized to accommodate multiple inputs.     

Rapoport's rule: time for an epitaph?

The christening of the decline in the geographic extent of species from high to low latitudes as Rapoport's rule was a bold step. Allowing for a variety of potentially significant complications to the interpretation of empirical studies, evidence that this is indeed a general pattern is, at the very least, equivocal. The present taxonomically and regionally biased set of studies lend support to the recent suggestion that the pattern is a local phenomenon being expressed primarily in the Palaearctic and Nearctic above latitudes of 40-50°N. Five hypotheses have been proposed to explain the generation of latitudinal declines in range size where they do occur, with the past heavy emphasis on a climatic variability mechanism being eroded. Evidence is accruing in support of more than one such mechanism. Whatever the generality of the `rule', it has undoubtedly served to stimulate a consideration of the role of spatial variation in range sizes in several areas of research in ecology and evolution.     

DNA vaccines: ready for prime time?

Since the discovery, over a decade and a half ago, that genetically engineered DNA can be delivered in vaccine form and elicit an immune response, there has been much progress in understanding the basic biology of this platform. A large amount of data has been generated in preclinical model systems, and more sustained cellular responses and more consistent antibody responses are being observed in the clinic. Four DNA vaccine products have recently been approved, all in the area of veterinary medicine. These results suggest a productive future for this technology as more optimized constructs, better trial designs and improved platforms are being brought into the clinic.     

Does cigarette smoking increase time to conception?

Data are reported on the relationship between cigarette smoking and other health-related behaviours and time to conception in a population-based sample of women who acted as a control group in a case-control study of twinning. Women who continued to smoke close to the time of conception took significantly longer to become pregnant than women who never smoked or stopped smoking before the year during which they attempted to conceive. A hierarchical regression analysis performed on time-to-conception data in women who continued to smoke in the year before conception provided weak evidence for a dose-response relationship between time to conception and number of cigarettes smoked per day. No significant relationships were found between time to conception and other health-related behaviours.     

Auditory neuroscience: a time for coincidence?

Mammals and birds appear to encode timing differences between the ears, a major cue for auditory localization, in fundamentally different ways. It now appears that results from different species can be accommodated within a single general framework.     

Pertussis control: time for something new?

Childhood acellular pertussis vaccines were licensed and implemented in the US in the 1990s following an effort to improve on the safety profile of whole-cell vaccines. However, waning of immunity from acellular vaccines may be driving the recent resurgence of pertussis, raising the need to consider new prevention strategies.