光流信息加工的神经基础

自体运动时,分布在视野内的景物在视网膜上的像旋转,扩张／收缩,浃动,构成光流刺激,光流信息的检测对于人或动物确定前进的方向,速度至关重要,已成为运动信息加工的一个研究热点。本文概括介绍了近年来心理物理和生理学两方面有关光流信息加工研究的主要进展,并讨论了光流信息分析的神经机制。     

Memory in monkeys as a function of preparatory interval and pattern complexity of matrix displays

Response speeds of eight monkeys (Macaca mulatta) were recorded as a measure of the strength of stimulus trace in remembering 1- to 4-light displays in a 4 × 4 matrix of translucent panels. The age of the animals, the length of the period between the warning signal and the stimulus, the duration of the delay between presenting the stimulus and allowing the animal to respond, and the complexity of the stimulus pattern were varied. Speed decreased for longer poststimulus delays and older subjects. The length of the foreperiod had a complex effect on response speed, and the display light position or pattern complexity had no reliable effect. These findings were contrasted with monkey memory measured by correct responses.     

Competition intensity as a function of resource availability in a semiarid ecosystem

Two field experiments were conducted using three dominant perennial species of the Chihuahuan Desert: Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a flat-stemmed succulent cactus). Two hypotheses concerning competition in arid plant communities were tested. (1) Marked resource partitioning with no interspecific competition could be expected since the three species belong to different life-forms, and that plant growth in deserts is basically limited by harsh environmental conditions. (2) Alternatively, resource scarcity (particularly water) will result in strong plant competition. In a 1-year removal experiment, water status and plant growth of the three species were monitored in twelve 10 m × 10 m plots randomized in three blocks and assigned to the following treatments: (a) removal of all species, except H. mutica; (b) removal of all species, except L. tridentata; (c) removal of all species, except O. rastrera, and (d) control without any manipulation. In a watering experiment, under two neighbourhood conditions (growing isolated or in associations of plants of the three species in plots of 20 m²), the water status of the three species and the growth of H.mutica and L.tridentata were studied for 32 days after an irrigation equivalent to 30 mm of rain, similar to a strong storm event at the site. In the removal experiment, where plants were free to capture water, no evidence of competition was observed. However, during the watering experiment, in which water was forced into the soil, competitive effects were observed. Associated individuals of L. tridentata had lower xylem water potentials and osmotic potentials (OPs) and produced shorter twigs and less leaves and nodes. Although less pronounced, neighbours also had a negative effect on the OP in O. rastrera. According to these results, the intensity of the interspecific competition for water seems to depend on the level of resource availability in the soil. Thus, the validity of the two hypotheses tested in this study also depends on the level of resources. Competition could be absent or very low in years of low precipitation, as in the year of this study (173 mm against a 25-year average of 264 mm). However, when soil water availability is high, e.g. following heavy rain, the negative interactions between species could be more intense. Received: 3 October 1997 / Accepted: 23 March 1998     

Modeling boundary vector cell firing given optic flow as a cue

Boundary vector cells in entorhinal cortex fire when a rat is in locations at a specific distance from walls of an environment. This firing may originate from memory of the barrier location combined with path integration, or the firing may depend upon the apparent visual input image stream. The modeling work presented here investigates the role of optic flow, the apparent change of patterns of light on the retina, as input for boundary vector cell firing. Analytical spherical flow is used by a template model to segment walls from the ground, to estimate self-motion and the distance and allocentric direction of walls, and to detect drop-offs. Distance estimates of walls in an empty circular or rectangular box have a mean error of less than or equal to two centimeters. Integrating these estimates into a visually driven boundary vector cell model leads to the firing patterns characteristic for boundary vector cells. This suggests that optic flow can influence the firing of boundary vector cells.     

Cardiorespiratory responses of sedentary college women as a function of training intensity.

Twenty-seven sedentary college women trained on a treadmill 3 times weekly over a 9-wk experimental period. Subjects exercised at a heart rate (HR) of either 50 or 65% of the HR reserve added to the resting HR with the duration of each session limited to the time required to elicit 1,000 beats above the resting value. Treadmill speed was adjusted automatically to maintain the prescribed exercise heart rate (EHR) within +/- 5 beats-min(-1). A comparison of the pretraining and posttraining results revealed that both training intensities caused significant increases in VO2max (1-min(-1) and ml-kg(-1)-min(-1)), V at VO2max, and O2 pulse at VO2max, and a significant decrease in VEO2 at VO2max. There was no alteration in EHR at VO2max for either intensity. For every dependent variable in which training effects were noted, the absolute gain made by the subjects training at the 65% intensity was greater than for those exercising at 50%. In no instance, however, was the difference between groups statistically significant. It was concluded that training at an EHR of either 50 or 65% of the HR reserve plus resting HR is sufficient to elicit a training response.     

Changes in landing biomechanics during a fatiguing landing activity.

The objective of this study was to investigate the effects of LE fatigue on ground impact force, LE kinematics, and LE kinetics during landing. Ground reaction force (GRF), kinematic, and electromyogram (EMG) data were collected from 12 male subjects during a fatiguing landing activity (FLA). This activity allowed not only the biomechanical differences between unfatigued and fatigued landings to be determined, but also the time history of multiple biomechanical variables as fatigue progressed. EMG mean frequency analysis using data collected immediately before and after the FLA indicated that subjects experienced fatigue of the quadriceps muscles. Results indicated a decrease in ground impact force and an increase in maximum joint flexion during landing with fatigue. Joint impulse values were consistent with a distal to proximal redistribution of extensor moment production. Potential reasons for this redistribution are discussed. A trend reversal in hip and ankle impulse during the activity suggest a change in landing strategy as fatigue progressed. The data also suggest that the measured changes in landing biomechanics may have been influenced by other factors, in addition to fatigue, such as a neuromuscular protective mechanism to decrease impact force magnitude.     

Cardinal directions for visual optic flow.

As we move through our environment, the flow of deforming images on the retinae provides a rich source of information about the three-dimensional structure of the external world and how to navigate through it. Recent evidence from psychophysical [1] [2] [3] [4], electrophysiological [5] [6] [7] [8] [9] and imaging [10] [11] studies suggests that there are neurons in the primate visual system - in the medial superior temporal cortex - that are specialised to respond to this type of complex 'optic flow' motion. In principle, optic flow could be encoded by a small number of neural mechanisms tuned to 'cardinal directions', including radial and circular motion [12] [13]. There is little support for this idea at present, however, from either physiological [6] [7] or psychophysical [14] research. We have measured the sensitivity of human subjects for detection of motion and for discrimination of motion direction over a wide and densely sampled range of complex motions. Average sensitivity was higher for inward and outward radial movement and for both directions of rotation, consistent with the existence of detectors tuned to these four types of motion. Principle component analysis revealed two clear components, one for radial stimuli (outward and inward) and the other for circular stimuli (clockwise and counter-clock-wise). The results imply that the mechanisms that analyse optic flow in humans tend to be tuned to the cardinal axes of radial and rotational motion.     

Visual guidance based on optic flow: a biorobotic approach.

This paper addresses some basic questions as to how vision links up with action and serves to guide locomotion in both biological and artificial creatures. The thorough knowledge gained during the past five decades on insects' sensory-motor abilities and the neuronal substrates involved has provided us with a rich source of inspiration for designing tomorrow's self-guided vehicles and micro-vehicles, which will be able to cope with unforeseen events on the ground, under water, in the air, in space, on other planets, and inside the human body. Insects can teach us some useful tricks for designing agile autonomous robots. Since constructing a "biorobot" first requires exactly formulating the biological principles presumably involved, it gives us a unique opportunity of checking the soundness and robustness of these principles by bringing them face to face with the real physical world. "Biorobotics" therefore goes one step beyond computer simulation. It leads to experimenting with real physical robots which have to pass the stringent test of the real world. Biorobotics provide us with a new tool, which can help neurobiologists and neuroethologists to identify and investigate worthwhile issues in the field of sensory-motor control. Here we describe some of the visually guided terrestrial and aerial robots we have developed since 1985 on the basis of our biological findings. All these robots behave in response to the optic flow, i.e., they work by measuring the slip speed of the retinal image. Optic flow is sensed on-board by miniature electro-optical velocity sensors. The very principle of these sensors was based on studies in which we recorded the responses of single identified neurons to single photoreceptor stimulation in a model visual system: the fly's compound eye.     

Intensity contrast as a crucial cue for butterfly landing

Papilio butterflies use a tetrachromatic color vision to discriminate a rewarding flower, approach, land and take nectar from the flower. In the course of further analyzing their foraging behavior in a laboratory condition, we found that some butterflies could not land on the target flower even they discriminated and tried to land on it, especially when the target was dark. This phenomenon, which we call “landing suppression”, indicates that the cue for landing differs from the cue for visually locating a flower. We hypothesized that a possible cue for landing was intensity contrast between the target and background, and have initiated to test this hypothesis. We tested the butterflies’ landing behavior to targets of various colors and intensities presented on background of black or various densities of gray. As a result, the landing was most strongly suppressed when the intensity contrast was close to zero irrespective of the target colors, suggesting that the butterflies used the target-background intensity contrast when landing.     

Timing and function of chitin synthesis in yeast.

A temperature-sensitive mutant of Saccharomyces cerevisiae, L-2-42, is blocked at 37 C at a stage of the cell cycle prior to septum formation. When single cells of the mutant are allowed to bud at 37 C in a medium containing tritiated glucose, a large incorporation of radioactivity into chitin takes place. Thus, the synthesis of chitin, the major component of the primary septum, is initiated in a phase of the cell cycle which precedes septum closure. This early period of chitin synthesis is not required for emergence and growth of buds because, in the wild type, budding takes place normally in the presence of concentrations of polyoxin D that effectively and specifically prevent chitin formation. However, at a later time a majority of these cells lyse, presumably because of the inability to form a septum. Polyoxin D also prevents the appearance of enhanced fluorescence at the junction between mother cell and bud, as observed in the presence of a brightener. Therefore, the fluorescence is due to chitin and its presence at the base of very early buds indicates that chitin synthesis begins at or shortly after bud emergence. A scheme for chitin synthesis and primary septum formation which embodies these and other results is presented.     

Fear responses in domestic chicks as a function of the social environment

The open field or novel environment has been used to assess fear in many species but its validity for the domestic fowl has recently been questioned. Based primarily on experiments which involved manipulation of the social environment Gallup and Suarez proposed that, contrary to an emotionality or fear interpretation, “open–field behaviour in chickens represents a compromise between opposing tendencies to reinstate contact with conspecifics and to minimize detection in the face of possible predation”. Predictions which can be made from the Gallup and Suarez model and from the fear hypothesis were tested by examining the effects of manipulating the social environment, during rearing and testing, on the open–field, hole–in–the–wall box and tonic immobility responses of domestic chicks. The results were inconsistent with predictions made from the Gallup and Suarez model but they conformed to the fear hypothesis. Furthermore, they were consistent with the majority of findings reported in the literature. Thus, while the opposing tendencies of reinstatement and predator evasion are, almost undoubtedly, important in many situations there remains considerable evidence for the role of fear in regulating the responses of domestic chicks to novel environments such as the open field. The two interpretations should not be considered mutually incompatible.     

Plant allocation of carbon to defense as a function of herbivory,light and nutrient availability

We use modeling to determine the optimal relative plant carbon allocations between foliage, fine roots, anti-herbivore defense, and reproduction to maximize reproductive output. The model treats these plant components and the herbivore compartment as variables. Herbivory is assumed to be purely folivory. Key external factors include nutrient availability, degree of shading, and intensity of herbivory. Three alternative functional responses are used for herbivory, two of which are variations on donor-dependent herbivore (models 1a and 1b) and one of which is a Lotka–Volterra type of interaction (model 2). All three were modified to include the negative effect of chemical defenses on the herbivore. Analysis showed that, for all three models, two stable equilibria could occur, which differs from most common functional responses when no plant defense component is included. Optimal strategies of carbon allocation were defined as the maximum biomass of reproductive propagules produced per unit time, and found to vary with changes in external factors. Increased intensity of herbivory always led to an increase in the fractional allocation of carbon to defense. Decreases in available limiting nutrient generally led to increasing importance of defense. Decreases in available light had little effect on defense but led to increased allocation to foliage. Decreases in limiting nutrient and available light led to decreases in allocation to reproduction in models 1a and 1b but not model 2. Increases in allocation to plant defense were usually accompanied by shifts in carbon allocation away from fine roots, possibly because higher plant defense reduced the loss of nutrients to herbivory.     

Differential use of sensory information in sexual behavior as a function of gender

Olfactory information is critical to mammalian sexual behavior. Based on parental investment theory the relative importance of olfaction compared with vision, touch, and hearing should be different for human males and females. In particular, because of its link to immunological profile and offspring viability, odor should be a more important determinant of sexual choice and arousal for females than for males. To test this hypothesis a questionnaire was developed and administered to 332 adults (166 males, 166 females). Subjects used a 1–7 scale to indicate how much they agreed with a series of statements concerning the importance of olfactory, visual, auditory, and tactile information for their sexual responsivity. The data reveal that males rated visual and olfactory information as being equally important for selecting a lover, while females considered olfactory information to be the single most important variable in mate choice. Additionally, when considering sexual activity, females singled out body odor from all other sensory experiences as most able to negatively affect desire, while males regarded odors as much more neutral stimuli for sexual arousal. The present results support recent findings in mice and humans concerning the relation of female preferences in body odor and major histocompatibility complex (MHC) compatibility and can be explained by an evolutionary analysis of sex differences in reproductive strategies. This work represents the first direct examination of the role of different forms of sensory information in human sexual behavior.     

Integral energy as a measure of soil-water availability

The available water capacity is the most commonly used parameter to quantify the amount of water readily available to plants. However, it does not directly describe the energy requirements of the plant to remove a unit amount of water from the soil at various moisture contents within the available range. We present the integral energy concept as an attempt to quantify this. It is calculated from the integral of a soil's water-retention curve. We demonstrate the calculation for different types of soil. The integral energy provides useful information regarding the amount of energy, and hence the availability of water to plants. The value appears to be more correlated with basic soil physical properties, such as clay and sand content, compared with the conventional available water capacity.