A dynamic model of thoracic differentiation for the control of turning in the stick insect

Leg movements of stick insects (Carausius morosus) making turns towards visual targets are examined in detail, and a dynamic model of this behaviour is proposed. Initial results suggest that front legs shape most of the body trajectory, while the middle and hind legs just follow external forces (Rosano H, Webb B, in The control of turning in real and simulated stick insects, vol. 4095, pp 145–156, 2006). However, some limitations of this explanation and dissimilarities in the turning behaviour of the insect and the model were found. A second set of behavioural experiments was made by blocking front tarsi to further investigate the active role of the other legs for the control of turning. The results indicate that it is necessary to have different roles for each pair of legs to replicate insect behaviour. We demonstrate that the rear legs actively rotate the body while the middle legs move sideways tangentially to the hind inner leg. Furthermore, we show that on average the middle inner and hind outer leg contribute to turning while the middle outer leg and hind inner leg oppose body rotation. These behavioural results are incorporated into a 3D dynamic robot simulation. We show that the simulation can now replicate more precisely the turns made by the stick insect. This work was supported by CONACYT México and the European Commission under project FP6-2003-IST2-004690 SPARK.     

Human Dimensions of Earthworm Invasion in the Adirondack State Park

The invasion of exotic earthworms in the Northern Forest of the United States alters carbon and nitrogen cycles and reduces forest litter and native plant cover. Humans are the principal agents of dispersal, spreading earthworms both inadvertently via horticulture, land disturbance, and in the tires and underbodies of vehicles, and voluntarily through composting and the improper disposal of fish bait. A study in Webb, NY—a town located within the Adirondack State Park, one of the most celebrated cultural and ecological regions in the US—exposes the human dimensions of earthworm invasion. Environmental history research, interviews with residents and bait sellers, and a mail survey of town residents show that positive attitudes towards earthworms and their ecological effects lead to casual disposal or use of them. Earthworm use is a strong cultural practice and the risk of their continued introduction in the Adirondacks is high.     

Competing political visions and Bolivia’s unfinished revolution

In Bolivia, there is a growing conflict between indigenous peoples and multinational corporations, particularly those in extractive industries. Evo Morales’s government is in the middle of the conflict and that makes the ongoing political situation very confusing. The ambiguity derives from the fact that the popular mobilizations did not go far enough; they were not sufficient to reconstitute a stable, alternative form of political rule.     

Points of departure for a constructive critique of the Bolivarian Revolution

From what Left position, both intellectually and politically, does one formulate a critique of the Chávez-led Bolivarian Revolution without aligning with a right-wing opposition? For starters, we need reliable evidence of the achievements, problems, and mistakes of the Bolivarian project. At the same time, any engagement with social change in Venezuela necessitates attention to one’s positionality as well as scholarly and activist categories of analysis and practice.     

Bats and frogs and animals in between: evidence for a common central timing mechanism to extract periodicity pitch

Widely divergent vertebrates share a common central temporal mechanism for representing periodicities of acoustic waveform events. In the auditory nerve, periodicities corresponding to frequencies or rates from about 10 Hz to over 1,000 Hz are extracted from pure tones, from low-frequency complex sounds (e.g., 1st harmonic in bullfrog calls), from mid-frequency sounds with low-frequency modulations (e.g., amplitude modulation rates in cat vocalizations), and from time intervals between high-frequency transients (e.g., pulse-echo delay in bat sonar). Time locking of neuronal responses to periodicities from about 50 ms down to 4 ms or less (about 20–300 Hz) is preserved in the auditory midbrain, where responses are dispersed across many neurons with different onset latencies from 4–5 to 20–50 ms. Midbrain latency distributions are wide enough to encompass two or more repetitions of successive acoustic events, so that responses to multiple, successive periods are ongoing simultaneously in different midbrain neurons. These latencies have a previously unnoticed periodic temporal pattern that determines the specific times for the dispersed on-responses.