Type Of Spatial Mechanism Research Articles

The Fixed Slope Rule: An Inter-Specific Study

There are two broad mechanisms by which animals can assess risk when deciding whether to flee: temporally and spatially. Animals that employ temporal mechanisms use predator speed to gauge threat. In contrast, those that use spatial mechanisms use the distance to the predator as an indication of danger. Traditionally, this was viewed as a fixed distance. Recently, a new type of spatial mechanism was proposed that focused on animals initiating flight at a fixed ratio of the distance at which they first responded to the threat. Our study investigated the consistency of this slope among three species: the Eastern gray kangaroo (Macropus giganteus), the Australian wood duck (Chenonetta jubata), and the Australian magpie (Gymnorhina tibicen). We found that these species exhibited statistically indistinguishable slopes from each other and the 0.44 slope that was initially reported in another species. Our results further support the assumption that escape decisions are dynamic. Future studies should determine the ubiquity of this fixed ratio.

Dynamic characteristics of spatial mechanisms coding contour structures.

Psychophysical thresholds for the detection of luminance targets improve significantly when the targets are presented in a specific context of spatially separated, collinear inducing stimuli defining visual contours. This phenomenon is generally referred to as a special case of detection facilitation called spatial facilitation. Spatial facilitation has been observed with luminance-defined. achromatic stimuli on achromatic backgrounds as well as with targets and inducers defined by colour contrast. This paper reviews psychophysical results from detection experiments with human observers showing the conditions under which spatially separated contour inducers facilitate the detection of simultaneously presented target stimuli. The findings point towards two types of spatial mechanisms: (i) Short-range mechanisms that are sensitive to narrowly spaced stimuli of small size and, at distinct target locations, selective to the contrast polarity of targets and inducers. (ii) Long-range mechanisms that are triggered by longer stimuli, generate facilitation across wider spatial gaps between targets and inducers, and are insensitive to their contrast polarity. Spatial facilitation with chromatic stimuli requires a longer inducer exposure than spatial facilitation with achromatic stimuli, which is already fully effective at inducer exposures of 30 ms. This difference in temporal dynamics indicates some functional segregation between mechanisms for colour and luminance contrast in spatial coding. In general, spatially induced detection facilitation can to a large extent be explained by mechanisms involving from-short-to-long-range interactions between cortical detectors.

Gross Motion Attributes of Certain Spatial Mechanisms

A new method is presented by which positions of peculiar kinematic interest, such as ends of travel, locking positions and points of “uncertainty,” in certain types of spatial mechanisms can be readily ascertained. This method is based upon an analysis of the curves of intersection of the surfaces generated by points in the mechanisms, and is there related in such a manner as to render it useful both in determining the positiona interrelationships of components of the mechanisms, and in classifying the mechanism according to its motion.

Acceleration Analysis of Spatial Four-Link Mechanisms

Acceleration analysis of a spatial four-link mechanism with one revolute pair and three cylindrical pairs of general proportions is presented here; results are expressed in concise algebraic forms which are well adapted to either manual or programmed computation. It is believed that the method employed in this paper may be applied to acceleration analysis of other types of spatial mechanisms and that it may serve as an alternative to the well-known vector method.