The inverse intensity effect is not lost with stimuli in apparent motion

The inverse relationship between the visible persistence of a briefly presented stimulus and its intensity is well established for static displays. However, with non-static displays, this relationship is only partially reported by previous studies. In order to clarify this topic, we investigated the effect of luminance on the visible persistence of a stimulus in apparent motion. Assuming that persistence duration is a normally distributed random variable, we studied whether the mean persistence of a stimulus could be systematically varied by varying its luminance. Our paradigm permits evaluation of this effect without changing the temporal interval between two successive presentations of the stimulus, thus avoiding the potential influence of this latter factor on persistence. Our results show that the inverse intensity effect still occurs at each of the successive locations of a stimulus in apparent motion. In addition, we provide evidence that increasing the spatial separation between the successive presentations, and decreasing the background luminance, result both in longer persistence duration. Altogether, these findings favour the hypothesis that persistence is actively suppressed by inhibitory interactions between adjacent neural zones.     

点的速度合成定理在牵连运动为平面运动时的应用

把作平面运动的实际刚体概念扩展成一个作平面运动的抽象质点系,以此为动系,用刚体平面运动理论来求解无载体牵连点在平面上的合成运动问题,并对此解法加以验证.     

Estimating the velocity of briefly presented moving stimuli

The ability of human subjects to estimate the velocity of briefly presented moving stimuli was studied in a prediction-of-collision experiment. After the disappearance of the moving target the subject had to press a button at the moment the target would reach a predetermined position in the visual field. Four velocities of the moving target were used -6 degrees/s, 10 degrees/s, 14 degrees/s, and 20 degrees/s. For each velocity there were five exposure distances: 0.5, 1.0, 2.0, 3.0 and 4.0 degrees and four concealment distances: 6, 8, 10 and 12 degrees. For the large exposure distances a linear dependence of the response time on the concealment time was observed. This dependence was not linear for exposure durations less than 100 ms. The response time increased in these cases. Despite the common character of the results obtained with different subjects there were clear individual differences most probably due to differences in subjective velocity scales and individual mechanisms of motion extrapolation and organization of motor responses.     

Inhibition of return is not detected using illusory line motion

Inhibition of return (IOR) is the name that has been assigned to a response time (RT) delay to a stimulus presented at a recently stimulated spatial location. A commonly held explanation for the origins of IOR is that perceptual processing in inhibited and that this inhibition translates into slower RT. Three experiments with 10 subjects were used to directly test this perceptual explanation. The first two experiments assessed the level of perceptual facilitation present in the IOR paradigm using the frequency and latency of illusory line motion judgments. Contrary to the predictions of the perceptual view, the line motion and RT measures revealed only speeded processing at previously stimulated spatial locations. Experiment 3 required a simple detection response and used the same stimulus and timing parameters as those in Experiments 1 and 2. IOR was present, replicating the recent finding that judgments based on perceptual qualities of the stimulus do not demonstrate a RT delay, whereas simple detection tasks do show RT inhibition at previously stimulated locations. These findings are discussed in relation to a number of hypotheses about the origin of the RT delay.     

Position and velocity coupling of postural sway to somatosensory drive

Light touch contact of a fingertip to a stationary surface provides orientation information that enhances control of upright stance. Slight changes in contact force at the fingertip lead to sensory cues about the direction of body sway, allowing attenuation of sway. In the present study, the coupling of postural sway to a moving contact surface was investigated in detail. Head, center of mass, and center of pressure displacement were measured as the contact surface moved rhythmically at 0.1, 0.2, 0.4, 0.6, and 0.8 Hz. Stimulus amplitude decreased with frequency to maintain peak velocity constant across frequency. Head and body sway were highly coherent with contact surface motion at all frequencies except 0.8 Hz, where a drop-off in coherence was observed. Mean frequency of head and body sway matched the driving frequency 相似文献   

Learned patterns of action-effect anticipation contribute to the spatial displacement of continuously moving stimuli.

When participants control the horizontal movements of a stimulus and indicate its vanishing point after it unexpectedly vanishes, the perceived vanishing point is displaced beyond the actual vanishing point, and the size of the displacement is directly related to the action-effect anticipation one has to generate to successfully control the stimulus. The present experiments examined whether learning a pattern of action-effect anticipation would later impact one's perception of moving stimuli. While 1 participant (the controller) controlled a dot's movements across a computer screen, another (the observer), who could neither see nor hear the controller, watched the dot's movements on a separate monitor. When the dot unexpectedly vanished, the observer indicated the vanishing point. After 40 trials, participants switched roles. While serving as observers, all participants generated forward displacements, but those who did so after acquiring control experience produced larger displacement. Subsequent experiments indicated the larger displacement was due to action-effect anticipation the participants learned while either controlling the dot or observing another do so. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ocular responses to motion parallax stimuli: the role of perceptual and attentional factors

When human subjects are presented with visual displays consisting of random dots moving sideways at different velocities, they perceive transparent surfaces, moving in the same direction but located at different distances from themselves. They perceive depth from motion parallax, without any additional cues to depth, such as relative size, occlusion or binocular disparity. Simultaneously, large-field visual motion triggers compensatory eye movements which tend to offset such motion, in order to stabilize the visual image of the environment. In a series of experiments, we investigated how such reflexive eye movements are controlled by motion parallax displays, that is, in a situation where a complete stabilization of the visual image is never possible. Results show that optokinetic nystagmus, and not merely active visual pursuit of singular elements, is triggered by such displays. Prior to the detection of depth from motion parallax, eye tracking velocity is equal to the average velocity of the visual image. After detection, eye tracking velocity spontaneously matches the slowest velocity in the visual field, but can be controlled by attentional factors. Finally, for a visual stimulation containing more than three velocities, subjects are no longer able to perceptually dissociate between different surfaces in depth, and eye tracking velocity remains equal to the average velocity of the visual image. These data suggest that, in the presence of flow fields containing motion parallax, optokinetic eye movements are modulated by perceptual and attentional factors.     

In dubio pro defensio: Initial activation of conditioned fear is not cue specific.

This study explored the time course of conditioned fear response expression. Two neutral male facial expressions served as conditioned stimuli (CS) in a differential trace conditioning that involved either an aversive (n=14) or a nonaversive (n=12) unconditioned stimulus (UCS) in a between-subjects design. Skin conductance response (SCR) to the CSs and startle response magnitudes to acoustic probes presented at early (250 ms) or late (1,750 ms) probe times after CS onset were measured. As expected, conditioned SCR discrimination was observed in both aversive and nonaversive learning, whereas the conditioned potentiation of the startle response was only observed for the aversive UCS condition. Interestingly, conditioned startle discrimination was specific for the later probe time. In contrast, conditioned fear potentiation of the startle response at the early probe time was equally pronounced for CS+ and CS-. These findings suggest that fear-eliciting neural structures are rapidly activated in fear learning, whereas the expression of inhibitory conditioning requires more time, presumably reflecting the involvement of cortical top-down control processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The contribution of spatial cues to memory: Direction, but not cue, changes support response reversal learning.

In four experiments, rats were trained on a response problem followed by three reversals. Rats that changed rooms between acquisition and reversals learned the reversals in fewer trials than rats that remained in the same room, even when distal visual cues were limited. Changes in orientation, even in the same room, also facilitated response reversal learning. The advantage observed with changes in orientation across reversals does not appear to be due to differences in local views or to different start positions. Direction changes, but not cue changes, may support response reversal learning by taking advantage of the natural interaction between responses and direction when one map is used. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Water deprivation enhances fear conditioning to contextual, but not discrete, conditional stimuli in rats.

Water-deprived and nondeprived rats were fear conditioned with a discrete tone CS and an aversive footshock unconditioned stimulus/stimuli (UCS). 24 and 48 hrs following conditioning, conditional fear to the tone CS and the context cues of the conditioning chamber, respectively, were assessed by measuring freezing behavior. Water deprivation had no effect on baseline responding to either tone or contextual stimuli. Following either 1 or 3 tone-shock pairings, however, water deprivation selectively enhanced conditional freezing to the contextual cues of the training chamber; conditional freezing to the tone was unaffected by water deprivation. These results are consistent with the view that water deprivation affects fear conditioning via an influence on the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lengthing the duration of response execution does not modulate blindness to action-compatible stimuli.

Action-compatible blindness refers to the finding that target stimuli are perceived less frequently if they are presented during the planning or execution of a compatible action (e.g., a left arrow presented during a left manual key press) than during an incompatible action (J. Müsseler and B. Hommel, 1997 a, b). We investigated the effect of lengthening the response execution phase in the action-compatible blindness paradigm by requiring subjects to tap a response key once or three times on the assumption that tapping three times would increase the duration of the execution phase of the response. Prior research (e.g., B. Stevanovski et al (2002); P. Wühr and J. Müsseler, [2001]) has shown that larger blindness effects are observed for targets presented during the execution phase of a response than after the response has been made. We investigated whether a larger blindness effect would be observed in the three-tap condition than in the one-tap condition, or whether lengthening the duration of the response would extend the time course of the blindness effect. Neither of these possibilities was supported by the data irrespective of whether the number of taps to be made was blocked or mixed within a block of trials. The results are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial performance is more sensitive to ethanol than nonspatial performance regardless of cue proximity

In rodents, ethanol produces a greater impact on the ability to perform spatial reference memory tasks than nonspatial reference memory tasks. Such evidence may reflect a selective disruption in the use of previously acquired spatial information. However, a nonmnemonic explanation has yet to be ruled out Tasks used to study ethanol's effects on spatial memory commonly require subjects to utilize distal, or extramaze, cues to respond correctly. In contrast, many previously used nonspatial tasks could be solved using cues located on the maze itself. Because ethanol has been shown to disrupt sensory processing, it is possible that previously observed differences in the effects of ethanol on spatial and nonspatial performance were actually due to differences in the proximity of relevant cues in the spatial and nonspatial tasks and not to a selective disruption in spatial memory. The present study compares the effects of ethanol on the performance of spatial and nonspatial reference memory tasks that require subjects to discriminate among extramaze cues for correct responding. Subjects were trained while sober to navigate to a goal arm on a 12-arm maze. In the spatial task, the goal arm was defined by its location with respect to a number of extramaze cues. In the nonspatial task, the goal arm was defined by the presence of a single extramaze cue located directly beyond the end of the arm. Subjects were tested under 1 of 4 doses of ethanol (0.0, 0.7, 1.4, and 2.1 g/kg). Performance on the nonspatial task was more resistant to the effects of ethanol than performance on the spatial task. The results suggest that differences in the effects of ethanol on spatial and nonspatial performance are not due to differences in the proximity of relevant cues in previously used spatial and nonspatial tasks.     

To work or not to work: that is not the question

We investigated the relationship between stereomicroscopic pit patterns and histological structures in 93 lesions of superficial depressed-type colorectal tumors to assess the possibility of diagnosing the level of invasion by the pit patterns. All 9 lesions with Va (amorphous)-type pit pattern showed massive invasion into the submucosal layer (sm2, sm3). Massive invasion into sm was observed in 66.7% (6/9) of lesions with Vi (irregular)-type pit pattern, whereas 22.2% (2/9) of the lesions invaded the shallow layer of the submucosa (sm1) and 11.1% (1/9) were limited to the mucosa. Among the lesions with pit patterns other than Va and Vi, 93. 3% (70/75) were limited to the mucosa, whereas 6.7% (5/70) invaded the submucosal layer, but all were limited to sm1. These findings show that stereomicroscopic analysis of the pit patterns of the superficial depressed-type colorectal tumors is useful for diagnosing the level of invasion.     

Cryptosporidium parvum is not transmissible to fish, amphibians, or reptiles

A recent report suggested that an isolate of Cryptosporidium parvum had established infections in fish, amphibians, and reptiles and raises concern that animals other than mammals might be a potential source of waterborne Cryptosporidium oocysts. To test this possibility, viable C. parvum oocysts, infectious for neonatal BALB/c mice, were delivered by gastric intubation to bluegill sunfish, poison-dart frogs, African clawed frogs, bearded dragon lizards, and corn snakes. Histological sections of the stomach, jejunum, ileum, and cloaca prepared from tissues collected on days 7 and 14 postinoculation (PI) were negative for Cryptosporidium developmental stages. However, inoculum-derived oocysts were detectable by fluorescein-labeled monoclonal antibody in feces of inoculated animals from day 1 to day 12 PI in fish and frogs, and up to day 14 PI in lizards. Snakes did not defecate for 14 days PI. Impression smears taken at necropsy on days 7 and 14 PI revealed C. parvum oocysts in the lumen of the cloaca of 2 fish and 1 lizard on day 7 PI only. Because tissue stages of the pathogen were not found, it appears that C. parvum was not heterologously transmitted to lower vertebrates. Under certain circumstances, however, such as after the ingestion of C. parvum-infected prey, lower vertebrates may disseminate C. parvum oocysts in the environment.     

Bilateral detection thresholds in dextrals and sinistrals reflect the more sensitive side of the nose, which is not lateralized

Recent studies have shed light on the different relationships between odorant receptor expression and the specification of neural identity in the olfactory systems of vertebrates and invertebrates. In mice, neuronal identity and axon guidance are specified by the single expressed olfactory receptor, whereas in C. elegans, neuronal identity appears to be independent of receptor expression.     

Allocation of spatial attention to emotional stimuli depends upon arousal and not valence.

Attentional allocation to emotional stimuli is often proposed to be driven by valence and in particular by negativity. However, many negative stimuli are also arousing leaving the question whether valence or arousal accounts for this effect. The authors examined whether the valence or the arousal level of emotional stimuli influences the allocation of spatial attention using a modified spatial cueing task. Participants responded to targets that were preceded by cues consisting of emotional pictures varying on arousal and valence. Response latencies showed that disengagement of spatial attention was slower for stimuli high in arousal than for stimuli low in arousal. The effect was independent of the valence of the pictures and not gender-specific. The findings support the idea that arousal affects the allocation of attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)