Caudo-rostral whole-field visual motion elicits forward locomotion in many organisms, including larval zebrafish. Here, we investigate the dependence on the latency to initiate this forward swimming as a function of the speed of the visual motion. We show that latency is highly dependent on speed for slow speeds (<10 mm s−1) and then plateaus for higher values. Typical latencies are >1.5 s, which is much longer than neuronal transduction processes. What mechanisms underlie these long latencies? We propose two alternative, biologically inspired models that could account for this latency to initiate swimming: an integrate and fire model, which is history dependent, and a stochastic Poisson model, which has no history dependence. We use these models to predict the behavior of larvae when presented with whole-field motion of varying speed and find that the stochastic process shows better agreement with the experimental data. Finally, we discuss possible neuronal implementations of these models.

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This paper presents a description of the adjective class in Dinka, and an exploration of its typological relevance to the existence of adjectives cross-linguistically. In Dinka, a subset of intransitive verbs can be defined by several morphophonological characteristics. The overwhelming majority of these are property concepts, despite the fact that the defining characteristics are unrelated to semantic properties. This suggests that property concepts provide a useful semantic context in the investigation of adjectives, even in languages where the adjective class is clearly a sub-class of another lexical category. While the analysis is based primarily on the Bor South dialect, it has been corroborated using evidence from other dialects. Therefore, it is likely that this characterization holds across the language.

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