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.     

Schistosomiasis in newly reclaimed areas in Egypt. 1-distribution and population seasonal fluctuation of intermediate host snails

Previous research indicates that response force increases with stimulus intensity in simple reaction time (SRT) tasks. This result contradicts the common view that the perceptual system activates the motor system via a punctate go signal of fixed size. An elaborated view assumes that the size of the go signal depends on stimulus intensity so that more intense stimuli yield more forceful responses. In order to examine the latter hypothesis, the present experiments manipulated stimulus duration as well as intensity. Response force increased with duration even beyond a critical value of about 60 ms at which stimulus duration no longer affected SRT. In addition, increasing the duration of a stimulus also increased the duration of force output. These findings argue against models with punctate transmission of activation to the motor system. Certain continuous models and variable output models with prolonged go signals provide acceptable accounts of these effects.     

Effects of stimulus duration and intensity on simple reaction time and response force.

Previous research indicates that response force increases with stimulus intensity in simple reaction time (SRT) tasks. This result contradicts the common view that the perceptual system activates the motor system via a punctate go signal of fixed size. An elaborated view assumes that the size of the go signal depends on stimulus intensity so that more intense stimuli yield more forceful responses. In order to examine the latter hypothesis, the present experiments manipulated stimulus duration as well as intensity. Response force increased with duration even beyond a critical value of about 60 ms at which stimulus duration no longer affected SRT. In addition, increasing the duration of a stimulus also increased the duration of force output. These findings argue against models with punctate transmission of activation to the motor system. Certain continuous models and variable output models with prolonged go signals provide acceptable accounts of these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus intensity dynamism.

The literature on the relationship between conditioned stimulus intensity and conditioned response magnitude—generally known by its Hullian name of "stimulus intensity dynamism" (Hull, 1949)—is reviewed. In contrast to the agreement found in the Russian literature as to the reality of this phenomenon, the results of Western research have often been negative or inconclusive. Possible reasons for these failures to obtain positive results are discussed, including the use of data obtained under conditions of extinction, choice of the GSR as the conditioned response, use of a restricted range of stimulus intensities, and failure to ensure that S discriminates the conditioned stimulus from other background stimuli. Also discussed is Perkins' (1953) hypothesis that stimulus intensity dynamism is due to generalization of inhibition from an unreinforced zero-intensity stimulus. (2 p. ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How do changes in speed affect the perception of duration?

Six experiments investigated how changes in stimulus speed influence subjective duration. Participants saw rotating or translating shapes in three conditions: constant speed, accelerating motion, and decelerating motion. The distance moved and average speed were the same in all three conditions. In temporal judgment tasks, the constant-speed objects seemed to last longer than the decelerating objects, which in turn seemed to last longer than the accelerating stimuli. In temporal reproduction tasks, the difference between accelerating and decelerating stimuli disappeared; furthermore, watching an accelerating shape lengthened the apparent duration of the subsequent (static) display. These results (a) suggest that temporal judgment and reproduction can dissociate for moving stimuli because the stimulus influences the apparent duration of the subsequent interval, and (b) constrain theories of time perception, including those which emphasize memory storage, those which emphasize the existence of a pacemaker-accumulator timing system, and those which emphasize the division of attention between temporal and non-temporal information processing. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Dependence of the transcranially induced silent period on the 'instruction set' and the individual reaction time

OBJECTIVES AND METHODS: We looked for influences of the experimental condition on the silent period (SP) from transcranial motor cortex stimulation and analyzed how the instruction given to the subject, as well as the individual reaction time, might affect the duration of the SP in the biceps brachii muscle. RESULTS: The duration of the SP was found to critically depend on the subject's voluntary reaction of the target muscle immediately after the stimulus. With low stimulus intensity and low background force, the duration of the silent period was significantly longer in 10 of 13 subjects (P = 0.002) when they were instructed to relax quickly after the stimulus rather than to maintain the the force at a constant level. A significant shortening of the SP (P = 0.02) was observed when the subjects were instructed to perform a rapid contraction of the target muscle in reaction to the cortical stimulus. With low stimulus intensity and high background force, the same influence of the instruction set was found in 6 of 13 subjects. When the subjects were left without precise instruction, the SP duration was unpredictable. In 10 subjects, the SP corresponded to that obtained with the instruction to maintain the force at a constant level. However, in 3 subjects it was prolonged to the value observed in the 'relax' instruction. With greater stimulus intensities, the effect of the instruction set on the SP duration was generally smaller. A significant prolongation was nevertheless found at low background forces with rapid relaxation (P < 0.001), and a significant shortening was found at high background forces with rapid contraction (P < 0.001) after the stimulus. The SP duration observed with 20% of maximal voluntary contraction (MVC) significantly correlated with the individual reaction time. No such correlation was found for the SP obtained with 80% MVC. The SP was slightly longer at 20% MVC, as compared to 80% MVC within each instruction group. This effect was significant (P < 0.05) at low stimulus intensities. CONCLUSIONS: Therefore, when assessing the SP duration for diagnostic purposes, not only the stimulus intensity but also the background force and the voluntary reaction must be standardized. Furthermore, great stimulus intensities and high background forces should be used to minimise the effects of instruction set and individual reaction time.     

Cross-modal equivalence in early infancy: Auditory–visual intensity matching.

To examine the hypothesis that young infants ignore differences between lights and sounds and instead respond to auditory and visual stimuli as more or less similar depending on their intensity, a cardiac habituation/dishabituation method with a test for stimulus generalization was employed. In 2 experiments, a total of 40 3-wk-old Ss were repeatedly presented with white-light followed by white-noise stimuli of different intensities. A U-shaped relationship between magnitude of cardiac response (CR) and loudness was found. In view of previous findings that without prior visual stimulation a monotonic increase in CR to the same range of auditory stimuli results, this finding of a significant quadratic relationship with loudness suggests that Ss were responding to the auditory stimuli in terms of their similarity to the previously presented visual stimulus. A separate group of 14 infants presented with a more intense visual stimulus exhibited a shift in the intensity at which a minimal CR occurred. Results of a study with 31 adults did not show any systematic relationship between CR and loudness, indicating that unlike infants, adults do not spontaneously make cross-modal matches of intensity. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Length of training, opportunities for comparison, and imprinting in chicks.

Trained 112 1-day-old domestic chicks for 30 or 60 min with 1 of 2 different stimuli. One-half of the Ss were given an opportunity to compare simultaneously the familiar stimulus with the novel one for the last 15 min of training. Subsequently all Ss were given a choice between the 2 stimuli. The opportunity to compare the 2 stimuli beforehand had no effect on Ss' behavior in the test. In contrast, the length of training was found to have a marked effect on the Ss; the longer they were exposed the more they attempted to approach the familiar stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time course of forward masking tuning curves in cat primary auditory cortex

Nonsimultaneous two-tone interactions were studied in the primary auditory cortex of anesthetized cats. Poststimulatory effects of pure tone bursts (masker) on the evoked activity of a fixed tone burst (probe) were investigated. The temporal interval from masker onset to probe onset (stimulus onset asynchrony), masker frequency, and intensity were parametrically varied. For all of the 53 single units and 58 multiple-unit clusters, the neural activity of the probe signal was either inhibited, facilitated, and/or delayed by a limited set of masker stimuli. The stimulus range from which forward inhibition of the probe was induced typically was centered at and had approximately the size of the neuron's excitatory receptive field. This "masking tuning curve" was usually V shaped, i.e., the frequency range of inhibiting masker stimuli increased with the masker intensity. Forward inhibition was induced at the shortest stimulus onset asynchrony between masker and probe. With longer stimulus onset asynchronies, the frequency range of inhibiting maskers gradually became smaller. Recovery from forward inhibition occurred first at the lower- and higher-frequency borders of the masking tuning curve and lasted the longest for frequencies close to the neuron's characteristic frequency. The maximal duration of forward inhibition was measured as the longest period over which reduction of probe responses was observed. It was in the range of 53-430 ms, with an average of 143 +/- 71 (SD) ms. Amount, duration and type of forward inhibition were weakly but significantly correlated with "static" neural receptive field properties like characteristic frequency, bandwidth, and latency. For the majority of neurons, the minimal inhibitory masker intensity increased when the stimulus onset asynchrony became longer. In most cases the highest masker intensities induced the longest forward inhibition. A significant number of neurons, however, exhibited longest periods of inhibition after maskers of intermediate intensity. The results show that the ability of cortical cells to respond with an excitatory activity depends on the temporal stimulus context. Neurons can follow higher repetition rates of stimulus sequences when successive stimuli differ in their spectral content. The differential sensitivity to temporal sound sequences within the receptive field of cortical cells as well as across different cells could contribute to the neural processing of temporally structured stimuli like speech and animal vocalizations.     

Stimulus compounding in interval timing: The modality–duration relationship of the anchor durations results in qualitatively different response patterns to the compound cue.

We have previously demonstrated that rats trained on a two-duration peak procedure in which two modal signals (i.e., tone and houselight) predicted probabilistic reinforcement availability at two times (10 s and 20 s) would respond in a scalar manner at a time between the trained durations in response to the simultaneous compound cue (tone + houselight). In these experiments, we evaluated whether this scalar response pattern would remain with greater relative separation between the anchor durations. Results revealed an effect of the modality–duration relationship, such that scalar responding was seen on compound trials in rats trained that the auditory stimulus signaled the shorter duration, whereas the visual stimulus signaled the longer duration, but not in the reverse condition. In rats showing scalar responding on compound trials, post hoc analyses demonstrated that the peak time of compound responding was most accurately predicted by the reinforcement probability weighted average of anchor peak times. In contrast, rats trained that the visual stimulus signaled the shorter duration, whereas the auditory stimulus signaled the longer duration, responded in a highly rightward skewed manner. In these rats, initiation of responding to the compound stimulus appeared to be controlled by the visual stimulus only, whereas response terminations reflected control by both modal stimuli. These latter data provide evidence of separate determinants of response initiation and termination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantitative analysis of the relation between gill amplitude and siphon duration in the defensive withdrawal reflex of Aplysia..

The defensive withdrawal reflex of the mantle organs (gill, siphon, and mantle shelf) of the marine mollusc Aplysia californica has been the subject of numerous studies investigating the cellular and molecular mechanisms of learning. In behavioral experiments, the reflex has been monitored by means of two different response measures, either siphon duration (in unrestrained, freely moving animals) or gill amplitude (in restrained preparations). It has generally been assumed that one component of the reflex provides a reliable index of the other. In the present study, we directly tested this assumption by simultaneously measuring both response parameters in the same experiment. Reflex response magnitude was varied in two ways: (a) by systematically varying stimulus intensity, and (b) by holding the stimulus intensity constant, but delivering stimuli at a rate that produced significant habituation. Using both measures we found that gill amplitude and siphon duration were highly correlated (average correlation?=?.90). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Startle reflex inhibition in the rat: Its persistence after extended repetition of the inhibitory stimulus.

Startle reflexes to intense sound bursts are inhibited by weak stimuli that briefly precede their elicitation. In 3 experiments, with 36 Long-Evans hooded rats, the startle stimulus (a 110-db tone burst) was presented 100 msec after the final link in a train of stimuli, the length of the train varying from 1 to 1,000, its repetition rate varying from 1 to 10 per sec, and its constituents being 40 db or 50 db white noise bursts of 25 msec duration. Inhibition was invariant across train length and repetition rate. In Exp IV, the startle stimulus was presented a variable interval after the final link, from 40 to 1,280 msec with 1 or 100 noise bursts (50 db) in the train. Inhibition developed more rapidly following the last member of the 100-stimulus train, suggesting a "priming" or sensitization effect of stimulus repetition, but its overall strength and subsequent rate of decay were not different in the 2 conditions. The general persistence of inhibition following these extended series of stimuli reveals that reflex inhibition must be the outcome of a fixed and obligatory process associated with sensory input. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amphetamine-induced disruption of latent inhibition depends on the nature of the stimulus

It is well documented that latent inhibition (LI), i.e. slower conditioning to a stimulus that had been repeatedly pre-exposed without consequences, compared to a non-pre-exposed stimulus, is prevented by amphetamine. Recently, we found that the effects of amphetamine on LI, as assessed in an off-baseline conditioned emotional response (CER) procedure, depend on the nature of the pre-exposed stimulus, irrespective of reinforcer intensity. Because these results contrast with a recent finding that a reduction in reinforcer intensity reversed amphetamine-induced attenuation of LI in an on-baseline CER procedure, the present study investigated the effects of amphetamine on LI as a function of the nature of the pre-exposed stimuli and shock intensity, using an on-baseline CER procedure. The effects of amphetamine on post-shock suppression of drinking as well as on activity, were monitored throughout the stages of the CER procedure. Experiment 1 used a 5 s steady light as the pre-exposed and conditioned stimulus, and two shock intensities in conditioning, and Experiment 2 used a 10 s flashing light and two shock intensities. Amphetamine disrupted LI with a steady light at both low and high shock intensities, but failed to disrupt LI with a flashing light at both shock intensities. In addition, the drug disrupted LI in Experiment 3, which increased the duration of the steady light to 10 s and used only low shock intensity, but failed to affect LI in Experiment 4 which used the flashing light on the background of darkness or of light, and only high shock intensity. The effects of amphetamine on LI were not related to its effects on behavioural suppression after footshock, or on activity.     

Multiple change-point analysis applied to the monitoring of Salmonella prevalence in Danish pigs and pork

The anterior and posterior exterolateral nuclei (ELa and ELp) of the mormyrid midbrain are thought to play a critical role in the temporal analysis of the electric discharge waveforms of other individuals. The peripheral electroreceptors receiving electric organ discharges (EODs) of other fish project through the brainstem to ELa via a rapid conducting pathway. EODs, composed of brief, but stereotyped waveforms are encoded as a temporal pattern of spikes. From previous work, we know that phase locking is precise in ELa. Here it is shown that evoked potentials recorded from ELp show a similar high degree of phase locking, although the evoked potentials last much longer. Single-unit recordings in ELp reveal two distinct populations of neurons in ELp: type I cells are responsive to voltage step functions, and not tuned for stimulus duration; type II cells are tuned to a specific range of stimulus durations. Type II cells are less responsive than type I cells, tend to respond with bursts of action potentials rather than with single spikes, have a longer latency, show weaker time locking to stimuli, and are more sensitive to stimulus polarity and amplitude. The stimulus selectivity of type II cells may arise from convergence of type I cell inputs. Despite the loss of rapid conduction between ELa and ELp, analysis of temporal features of waveforms evidently continues in ELp, perhaps through a system of labeled lines.     

Threshold setting by the surround of cat retinal ganglion cells

1. The slope of curves relating the log increment threshold to log background luminance in cat retinal ganglion cells is affected by the area and duration of the test stimulus, as it is in human pyschophysical experiments. 2. Using large area, long duration stimuli the slopes average 0-82 and approach close to 1 (Weber's Law) in the steepest cases. Small stimuli gave an average of 0-53 for on-centre units using brief stimuli, and 0-56 for off-centre units, using long stimuli. Slopes under 0-5 (square root law) were not found over an extended range of luminances. 3. On individual units the slope was generally greater for larger and longer test stimulus, but no unit showed the full extent of change from slope of 0-5 to slope of 1. 4. The above differences hold for objective measures of quantum/spike ratio, as well as for thresholds either judged by ear or assessed by calculation. 5. The steeper slope of the curves for large area, long duration test stimuli compared with small, long duration stimuli, is associated with the increased effectiveness of antagonism from the surround at high backgrounds. This change may be less pronounced in off-centre units, one of which (probably transient Y-type) showed no difference of slope, and gave parallel area-threshold curves at widely separated background luminances, confirming the importance of differential surround effectiveness in changing the slope of the curves. 6. In on-centre units, the increased relative effectiveness of the surround is associated with the part of the raised background light that falls on the receptive field centre. 7. It is suggested that the variable surround functions as a zero-offset control that sets the threshold excitation required for generating impulses, and that this is separate from gain-setting adaptive mechanisms. This may be how ganglion cells maintain high incremental sensitivity in spite of a strong maintained excitatory drive that would otherwise cause compressive response non-linearities.     

Backward pattern masking can vary as a nonmonotonic function of target duration: on the influence of intratraget metacontrast

The magnitude of backward masking is usually found to vary inversely with the amount of information about a target that is made available to the visual system. Contrary to these findings, we report a nonmonotonic relation between the magnitude of backward pattern masking and target duration. Specifically, masking decreased as target duration was increased to about 8 msec and, then, became more severe as target duration was further increased to a value of at least 40 msec. The occurrence of the nonmonotonic function depended on (a) the degree of definition of the target's edges, (b) the luminance levels within the target stimulus, and (c) the state of adaptation of the eye. It is hypothesized that the source of the nonmonotonic function was metacontrast interference that originated from within the target stimulus configuration. This hypothesis was supported by data that indicated that in the absence of any mask presentations, the apparent contrast between the target and its immediate background varied as a nonmonotonic function of target duration.     

How emotional auditory stimuli modulate time perception.

Emotional and neutral sounds rated for valence and arousal were used to investigate the influence of emotions on timing in reproduction and verbal estimation tasks with durations from 2 s to 6 s. Results revealed an effect of emotion on temporal judgment, with emotional stimuli judged to be longer than neutral ones for a similar arousal level. Within scalar expectancy theory (J. Gibbon, R. Church, & W. Meck, 1984), this suggests that emotion-induced activation generates an increase in pacemaker rate, leading to a longer perceived duration. A further exploration of self-assessed emotional dimensions showed an effect of valence and arousal. Negative sounds were judged to be longer than positive ones, indicating that negative stimuli generate a greater increase of activation. High-arousing stimuli were perceived to be shorter than low-arousing ones. Consistent with attentional models of timing, this seems to reflect a decrease of attention devoted to time, leading to a shorter perceived duration. These effects, robust across the 2 tasks, are limited to short intervals and overall suggest that both activation and attentional processes modulate the timing of emotional events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Directed attention prolongs the perceived duration of a brief stimulus

Stelmach, Herdman, and McNeil (1994) suggested recently that the perceived duration for attended stimuli is shorter than that for unattended ones. In contrast, the attenuation hypothesis (Thomas & Weaver, 1975) suggests the reverse relation between directed attention and perceived duration. We conducted six experiments to test the validity of the two contradictory hypotheses. In all the experiments, attention was directed to one of two possible stimulus sources. Experiments 1 and 2 employed stimulus durations from 70 to 270 msec. A stimulus appeared in either the visual or the auditory modality. Stimuli in the attended modality were rated as longer than stimuli in the unattended modality. Experiment 3 replicated this finding using a different psychophysical procedure. Experiments 4-6 showed that the finding applies not only to stimuli from different sensory modalities but also to stimuli appearing at different locations within the visual field. The results of all six experiments support the assumption that directed attention prolongs the perceived duration of a stimulus.     

Features of ipsilaterally evoked inhibition in the dorsal nucleus of the lateral lemniscus

The dorsal nucleus of the lateral lemniscus (DNLL) is a binaural nucleus whose neurons are excited by stimulation of the contralateral ear and inhibited by stimulation of the ipsilateral ear. Here we report on several features of the ipsilaterally evoked inhibition in 95 DNLL neurons of the mustache bat. These features include its dependence on intensity, its tuning and the types of stimuli that are capable of evoking it. Inhibition was studied by evoking discharges with the iontophoretic application of glutamate, and then evaluating the strength and duration of the inhibition of the glutamate evoked background activity produced by stimulation of the ipsilateral ear. Excitatory responses were evoked by stimulation of the contralateral ear with best frequency (BF) tone bursts. Glutamate evoked discharges could be inhibited in all DNLL neurons and the inhibition often persisted for periods ranging from 10 to 50 ms beyond the duration of the tone burst that evoked it. The duration of the persistent inhibition increased with stimulus intensity. Stimulus duration had little influence on the duration of the persistent inhibition. Signals as short as 2 ms suppressed discharges for as long as 30 ms after the signal had ended. The frequency tuning of the total period of inhibition and the period of persistent inhibition were both closely matched to the tuning evoked by stimulation of the contralateral ear. Moreover, the effectiveness of complex signals for evoking persistent inhibition, such as brief FM sweeps and sinusoidally amplitude and frequency modulated signals, was comparable to that of tone bursts at the neuron's excitatory BF, so long as the complex signal contained frequencies at or around the neuron's excitatory BF. We also challenged DNLL cells with binaural paradigms. In one experiment, we presented a relatively long (40 ms) BF tone burst of fixed intensity to the contralateral ear, which evoked a sustained discharge, and a shorter, 10 ms signal of variable intensity to the ipsilateral ear. As the intensity of the 10 ms ipsilateral signal increased, it generated progressively longer periods of persistent inhibition and thus the discharges were suppressed for periods far longer than the 10 ms duration of the ipsilateral signal. With interaural time disparities, ipsilateral signals that led contralateral signals evoked a persistent inhibition that suppressed the responses to the trailing contralateral signals for periods of a least 15 ms. This suggests that an initial binaural sound that favors the ipsilateral ear should suppress the responses to trailing sounds that normally would be excitatory if they were presented alone. We hypothesize a circuit that generates the persistent inhibition and discuss how the results with binaural signals support that hypothesis.     

Voltage dependence of rhythmic plateau potentials of pancreatic islet cells

The origin and control of glucose-induced rhythmic plateau potentials of pancreatic islet cells have been studied with intracellular microelectrodes in isolated mouse islets. Rapid changes of extracellular potassium concentration and direct electrical stimulation via a suction electrode were used to perturb islet cell membrane potentials. We show that brief depolarizing stimuli trigger permature plateau potentials, and brief hyperpolarizing currents abort endogenous plateaus. Both responses occur in an all-or-none manner, show a reciprocal relationship between stimulus strength and stimulus duration, have stimulus thresholds that approach zero at the time of the endogenous event, and completely reset the endogenous plateau rhythm. These results indicate that the plateau potentials are due to voltage-dependent regenerative mechanisms as in other electrically excitable tissues and implicate membrane potential or membrane ionic fluxes in the glucose-dependent pacemaker system that triggers their onset and offset.