Prior Stimulus Research Articles

Vestibular and proprioceptive estimation of imposed rotation and spatial updating in standing subjects

The aim of the study was to evaluate in standing subjects their perception of whole-body rotation and spatial updating, and to determine whether the brain uses mainly angular velocity or rotational duration to re-orient the body. Ten healthy blindfolded adults stood barefoot on a horizontal rotating platform. Participants had to maintain their balance while being passively rotated by a platform through 45°, 90°, 135°, 180° and 360°, clockwise (CW) and counter-clockwise (CCW). At the end of platform rotation, participants had to give their estimation of the angle. They then had to actively reproduce it in the opposite direction. Three different conditions were applied: one which involved different peak cosinusoidal angular velocity profiles (18°/s, 35°/s, 53°/s, 71°/s and 141°/s) at constant duration of stimulus (4s); one which involved different stimulus durations (1.25s, 2.5s, 3.75s, 5s and 10s) at constant peak velocity (57°/s); and one where subjects had to reproduce a specific angle without prior stimulus imposed by the platform. In the reproduction phase, results show overestimation of stimulus from −180° to 180° in all three conditions; however, ±360° rotations were underestimated only in the first two conditions. Comparing stimulus perception and reproduction, the perceived angle corresponded to that reproduced in the range from −180° to 180°; however, ±360° angles were correctly perceived but inaccurately reproduced. Thus, the interconnection between movement and information via the vestibular/proprioceptive systems is essential to evaluate the body position in space; however, the spatial errors show the key importance of sight in correcting the errors caused by the cue integration.

Leono Jovaišos asmenybės koncepcija: lyginamoji analizė

Docentas socialinių mokslų (edukologijos) daktarasŠiaulių universiteto Edukologijos katedraP. Višinskio g. 25, LT-76265.Tel. (8 41) 59 57 18El. paštas: roland.paulauskas@gmail.comStraipsnyje lyginama profesoriaus Leono Jovaišos asmenybės struktūros koncepcija su įvairių psichologinių pakraipų asmenybės teorijomis. Jame apžvelgiama L. Jovaišos polemika su užsienio asmenybės teoretikų idėjomis, pateikiama pastarųjų kritinė analizė ir nagrinėjami profesoriaus sudarytos asmenybės struktūros ypatumai ir jos pritaikymas edukologijos moksle. Daroma išvada, kad L. Jovaišos asmenybės teorija yra kokybiškai skirtinga nuo straipsnyje aptartų tyrėjų koncepcijų, pasižymi optimizmu bei edukologiniu pritaikymu ir yra išskirtina savo teleologiniu balansu. Asmenybės aktyvumo kryptį nulemia tiek vidiniai, tiek išoriniai mikro- ir makroaplinkos veiksniai. Lyginant su kitomis asmenybės teorijomis, L. Jovaišos asmenybės konstruktas yra vientisas ir nedalomas, o jo sudedamieji elementai vienas kitą sąlygoja ir papildo.

Distinct effects of perceptual quality on auditory word recognition, memory formation and recall in a neural model of sequential memory

Adults with sensory impairment, such as reduced hearing acuity, have impaired ability to recall identifiable words, even when their memory is otherwise normal. We hypothesize that poorer stimulus quality causes weaker activity in neurons responsive to the stimulus and more time to elapse between stimulus onset and identification. The weaker activity and increased delay to stimulus identification reduce the necessary strengthening of connections between neurons active before stimulus presentation and neurons active at the time of stimulus identification. We test our hypothesis through a biologically motivated computational model, which performs item recognition, memory formation and memory retrieval. In our simulations, spiking neurons are distributed into pools representing either items or context, in two separate, but connected winner-takes-all (WTA) networks. We include associative, Hebbian learning, by comparing multiple forms of spike-timing-dependent plasticity (STDP), which strengthen synapses between coactive neurons during stimulus identification. Synaptic strengthening by STDP can be sufficient to reactivate neurons during recall if their activity during a prior stimulus rose strongly and rapidly. We find that a single poor quality stimulus impairs recall of neighboring stimuli as well as the weak stimulus itself. We demonstrate that within the WTA paradigm of word recognition, reactivation of separate, connected sets of non-word, context cells permits reverse recall. Also, only with such coactive context cells, does slowing the rate of stimulus presentation increase recall probability. We conclude that significant temporal overlap of neural activity patterns, absent from individual WTA networks, is necessary to match behavioral data for word recall.

Spatiotemporally coherent motion direction perception occurs even for spatiotemporal reversal of motion sequence

Thus far, it has been pointed out that motion representation is completed in motion trajectory, and that motion representation interferes with a single physical input at a specific time and space in the motion trajectory. However, it has not been fully investigated whether the internal motion representation could interact with multiple physical inputs across time and space in motion trajectory. Thus, the current research investigated whether spatiotemporally coherent motion perception could be established in a situation involving the spatiotemporal reversal of motion sequences. In a five-point motion display, we found that the motion direction perception of the last two stimuli containing the spatiotemporal reversal was consistent with three preceding stimuli. This failure to perceive motion direction reversal occurred when the shapes of motion trajectory (to upper or lower) were randomly changed. Moreover, we confirmed that one preceding stimulus (three-point motion) was sufficient to produce the failure to perceive motion direction reversal, and the effect of the prior stimuli saturated when the preceding sequence contained two or more stimuli. These findings suggest that the flexible internal motion representation mechanisms reorganize the spatiotemporal irregularities in motion trajectory and establish spatiotemporally coherent motion perceptions.

Effects of prior stimulus and prior perception on neural correlates of auditory stream segregation

We examined whether effects of prior experience are mediated by distinct brain processes from those processing current stimulus features. We recorded event-related potentials (ERPs) during an auditory stream segregation task that presented an adaptation sequence with a small, intermediate, or large frequency separation between low and high tones (Deltaf), followed by a test sequence with intermediate Deltaf. Perception of two streams during the test was facilitated by small prior Deltaf and by prior perception of two streams and was accompanied by more positive ERPs. The scalp topography of these perception-related changes in ERPs was different from that observed for ERP modulations due to increasing the current Deltaf. These results reveal complex interactions between stimulus-driven activity and temporal-context-based processes and suggest a complex set of brain areas involved in modulating perception based on current and previous experience.

Reward rate optimization in two-alternative decision making: Empirical tests of theoretical predictions.

The drift-diffusion model (DDM) implements an optimal decision procedure for stationary, 2-alternative forced-choice tasks. The height of a decision threshold applied to accumulating information on each trial determines a speed-accuracy tradeoff (SAT) for the DDM, thereby accounting for a ubiquitous feature of human performance in speeded response tasks. However, little is known about how participants settle on particular tradeoffs. One possibility is that they select SATs that maximize a subjective rate of reward earned for performance. For the DDM, there exist unique, reward-rate-maximizing values for its threshold and starting point parameters in free-response tasks that reward correct responses (R. Bogacz, E. Brown, J. Moehlis, P. Holmes, & J. D. Cohen, 2006). These optimal values vary as a function of response-stimulus interval, prior stimulus probability, and relative reward magnitude for correct responses. We tested the resulting quantitative predictions regarding response time, accuracy, and response bias under these task manipulations and found that grouped data conformed well to the predictions of an optimally parameterized DDM.

Effects of stimulus–stimulus short-term memory associations in a Simon-like task

The Simon effect refers to faster responding when an irrelevant stimulus location corresponds with the response to a relevant stimulus attribute than when it does not. We investigated whether a memory-based Simon-like effect would occur when the irrelevant spatial attribute was associated with the stimulus during a prior task. In a first task, an association between colour and location was formed by requiring participants to count the occurrences of two colour stimuli, each of which was always presented in a left or right location. In a second task, the colour stimuli were presented centrally and mapped to left and right keypresses, with the mapping being inconsistent or consistent with the prior colour-location associations. A Simon-like effect was evident at the start of the second task, with performance being better when the established colour–position associations were consistent with the colour–response mapping than when they were not. This result indicates that stimulus–stimulus short-term memory associations formed during the first task transferred to the second task. For the remainder of the second task, the data showed a more conservative speed–accuracy criterion for the inconsistent condition than for the consistent condition, though a processing efficiency measure suggested that the prior stimulus–stimulus short-term associations may also continue to directly influence performance. Results suggest that simple declarative knowledge, as represented by stimulus–stimulus STM links, exerts less persistent transfer effects than procedural knowledge as provided by stimulus–response STM links.

Evidence for a Link Between the Extra-Retinal Component of Random-Onset Pursuit and the Anticipatory Pursuit of Predictable Object Motion

During pursuit of moving targets that temporarily disappear, residual smooth eye movements represent the internal (extra-retinal) component of pursuit. However, this response is dependent on expectation of target reappearance. By comparing responses with and without such expectation during early random-onset pursuit, we examined the temporal development of the extra-retinal component and compared it with anticipatory pursuit, another form of internally driven response. In an initial task (mid-ramp extinction), a moving, random-velocity target was initially visible for 100 or 150 ms but then extinguished for 600 ms before reappearing and continuing to move. Responses comprised an initial visually driven rapid rise in eye velocity, followed by a secondary slower increase during extinction. In a second task (short ramp), with identical initial target presentation but no expectation of target reappearance, the initial rapid rise in eye velocity was followed by decay toward zero. The expectation-dependent difference between responses to these tasks increased in velocity during extinction much more slowly than the initial, visually driven component. In a third task (initial extinction), the moving target was extinguished at motion onset but reappeared 600 ms later. Repetition of identical stimuli evoked anticipatory pursuit triggered by initial target offset. Temporal development and scaling of this anticipatory response, which was based on remembered velocity from prior stimuli, was remarkably similar to and covaried with the difference between mid-ramp extinction and short ramp tasks. Results suggest a common mechanism is responsible for anticipatory pursuit and the extra-retinal component of random-onset pursuit, a finding that is consistent with a previously developed model of pursuit.

Flash suppression and flash facilitation in binocular rivalry

We show that previewing one half image of a binocular rivalry pair can cause it to gain initial dominance when the other half is added, a novel phenomenon we term flash facilitation. This is the converse of a known effect called flash suppression, where the previewed image becomes suppressed upon rivalrous presentation. The exact effect of previewing an image depends on both the duration and the contrast of the prior stimulus. Brief, low-contrast prior stimuli facilitate, whereas long, high-contrast ones suppress. These effects have both an eye-based component and a pattern-based component. Our results suggest that, instead of reflecting two unrelated mechanisms, both facilitation and suppression are manifestations of a single process that occurs progressively during presentation of the prior stimulus. The distinction between the two phenomena would then lie in the extent to which the process has developed during prior stimulation. This view is consistent with a neural model previously proposed to account for perceptual stabilization of ambiguous stimuli, suggesting a relation between perceptual stabilization and the present phenomena.

Disruption of implicit perceptual memory by intervening neutral stimuli

After viewing directional motion, one is likely to perceive a subsequently presented directionally ambiguous motion as being in the same direction as the prior motion. The perceptual bias towards the most recent percept gradually develops as the interval between the prior stimulus and a subsequent test becomes longer. This form of positive bias, or priming, is created in an automatic fashion. It remain unclear how such perceptual bias could be eliminated by a stimulus manipulation. Here we examine whether presentation of a stimulus, which was neutral as to the competing perceptual interpretations, during the interval between prior and test stimuli, disrupts the development of the priming effect. In experiments with ambiguous motion, we used stationary gratings as the neutral stimuli, and in an experiment with binocular rivalry between orthogonal gratings, we used a plaid pattern consisting of the two rival gratings. In both cases, presenting the neutral stimuli reduced the perceptual bias. These findings show that the visual system dynamically calibrates its internal bias using a recent percept and that this internal bias can be nullified by presenting neutral stimuli.

Modulation of multisegmental monosynaptic responses in a variety of leg muscles during walking and running in humans

Motor responses evoked by stimulating the spinal cord percutaneously between the T11 and T12 spinous processes were studied in eight human subjects during walking and running. Stimulation elicited responses bilaterally in the biceps femoris, vastus lateralis, rectus femoris, medial gastrocnemius, soleus, tibialis anterior, extensor digitorum brevis and flexor digitorum brevis. The evoked responses were consistent with activation of Ia afferent fibres through monosynaptic neural circuits since they were inhibited when a prior stimulus was given and during tendon vibration. Furthermore, the soleus motor responses were inhibited during the swing phase of walking as observed for the soleus H-reflex elicited by tibial nerve stimulation. Due to the anatomical site and the fibre composition of the peripheral nerves it is difficult to elicit H-reflex in leg muscles other than the soleus, especially during movement. In turn, the multisegmental monosynaptic responses (MMR) technique provides the opportunity to study modulation of monosynaptic reflexes for multiple muscles simultaneously. Phase-dependent modulation of the MMR amplitude throughout the duration of the gait cycle period was observed in all muscles studied. The MMR amplitude was large when the muscle was activated whereas it was generally reduced, or even suppressed, when the muscle was quiescent. However, during running, there was a systematic anticipatory increase in the amplitude of the MMR at the end of swing in all proximal and distal extensor muscles. The present findings therefore suggest that there is a general control scheme by which the transmission in the monosynaptic neural circuits is modulated in all leg muscles during stepping so as to meet the requirement of the motor task.

On misattributing good remembering to a happy past: An investigation into the cognitive roots of nostalgia.

Reflections on the past are often accompanied by an experience of nostalgia, or positive sentiments about some prior stage of one's life. In the current study, we provide evidence suggesting that nostalgic experiences may occur because of positive feelings that accompany the act of successful recall, rather than reflecting the true nature of the past. In a series of experiments, we employed an encoding manipulation to cause some words to support more detailed recollections than others. In turn, we measured the effect of these manipulations on judgments of both pleasantness and the emotional valence of a prior stimulus encounter. We demonstrate that recollections rich in meaning are unique in biasing people to judge having previously seen a stimulus in an emotionally positive context. In contrast, pleasantness judgments appear to be guided primarily by perceptual fluency. Overall, our results are consistent with the notion that the subjective experience of nostalgia represents a misattribution of successful remembering to a pleasant past.

The inter-trial effects of stimulus and saccadic direction on prosaccades and antisaccades, in controls and schizophrenia patients

We investigated the influence of the direction of preceding saccadic trials on the latency of current prosaccades and antisaccades, in healthy subjects and patients with schizophrenia. When prosaccades and antisaccades were performed in separate, single-task blocks, we found that only prosaccades were delayed if the saccade in the prior trial was in the same direction, consistent with the expected directional effect from an 'inhibition of return'-like alternation advantage. However, both types of saccades were executed more quickly when the saccade in the penultimate trial was in the same direction, consistent with previous demonstrations of directional plasticity in monkeys. In blocks of randomly mixed prosaccades and antisaccades, the directional effects in healthy subjects were greatest when a prosaccade was preceded by an antisaccade, consistent with a summation of effects of alternation advantage (from the prior stimulus) and directional plasticity (from the prior saccade). Schizophrenic patients showed an additional phenomenon, a directionally specific inhibition of upcoming saccades by preceding antisaccades. These results suggest that saccades in humans are modulated by inter-trial effects attributable to both an 'inhibition of return'-like alternation advantage and directional plasticity.

Affective Assimilation and Contrast: Effects of Expectations and Prior Stimulus Exposure

The affective expectation model (AEM) proposes that expectations can cause both assimilation and contrast effects in affective experience. Specifically, the model contends that when a stimulus or experience is discrepant with an affective expectation, and an individual notices this discrepancy, affective reactions will be contrasted with the expectation. When the discrepancy goes unnoticed, however, it is anticipated that affective reactions will be assimilated toward the expectation. Two experiments were conducted to examine the potential role of prior stimulus exposure in the AEM. In both experiments, participants who had prior exposure to an expectation-inconsistent stimulus were more likely than controls to contrast their affective reactions with the affective expectation. Conversely, participants who had no prior exposure to the expectation-inconsistent stimulus were more likely than controls to assimilate their affective reactions toward the expectation. These findings demonstrate that prior stimulus exposure is an important situational moderator of the effect of affective expectations.

Identification and Bisection of Temporal Durations and Tone Frequencies: Common Models for Temporal and Nontemporal Stimuli.

Two experiments examined identification and bisection of tones varying in temporal duration (Experiment 1) or frequency (Experiment 2). Absolute identification of both durations and frequencies was influenced by prior stimuli and by stimulus distribution. Stimulus distribution influenced bisection for both stimulus types consistently, with more positively skewed distributions producing lower bisection points. The effect of distribution was greater when the ratio of the largest to smallest stimulus magnitude was greater. A simple mathematical model, temporal range frequency theory, was applied. It is concluded that (a) similar principles describe identification of temporal durations and other stimulus dimensions and (b) temporal bisection point shifts can be understood in terms of psychophysical principles independently developed in nontemporal domains, such as A. Parducci's (1965) range frequency theory.

Multiple effects of nicotine on behavior: a reply to Frenk and Dar (2003)

In Donny et al. (2003), we proposed the hypothesis that nicotine “may support behavior in two ways: by acting as a primary reinforcer and by directly potentiating the reinforcing effects of other stimuli.” Frenk and Dar (2003) favor an alternative hypothesis, that nicotine merely activates ongoing behavior, neither reinforcing specific behaviors nor facilitating the ability of other stimuli to do so. Here, we highlight some of the evidence for our hypothesis and explain why behavioral activation does not adequately account for the available data. Before presenting these data, we want to identify clearly the alternative hypothesis Frenk and Dar are proposing (Frenk and Dar 2000, 2003; Dar and Frenk 2002). They suggest that lever pressing is a consequence of prior food training and/or non-drug stimuli that either act as unconditioned reinforcers, or conditioned reinforcers (as a consequence of their pairing with food). From their perspective, the role of nicotine is simply to facilitate ongoing behavior, not to reinforce it. Nicotine acts as a reinforcer

Temporal gap detection in tactile channels

The ability of observers to detect temporal gaps in bursts of sinusoids or bursts of band-limited noise was measured to assess the temporal acuity of Pacinian (P) and non-Pacinian (NP) tactile information processing channels. The P channel was isolated by delivering high frequency sinusoids or high frequency noise through a large 1.5-cm2 contactor to the thenar eminence. The NP channels were isolated from the P channel by delivering these stimuli as well as stimuli with lower frequencies through a small 0.01-cm2 contactor to the same site. Gap detection thresholds were higher for gaps in noise than for gaps in sinusoids but did not differ among conditions designed to isolate P and NP channels. The finding that temporal acuity does not differ among channels supports the hypothesis that, after termination of a stimulus, the P and NP channels exhibit the same amount of neural persistence. Also consistent with this hypothesis are the earlier findings that the enhancement of the sensation magnitude of a stimulus by a prior stimulus (Verrillo and Gescheider, Percept Psychophys 18: 128–136, 1975) and the duration of sensation after the termination of a stimulus (Gescheider et al., J Acoust Soc Am 91: 1690–1696, 1992) are independent of stimulus frequency. One important implication of this hypothesis, if true, is that the presence of temporal summation in the P channel and its absence in the NP channels, results, not from the lack of neural persistence in the NP channels, but instead, in marked contrast to the P channel, from the lack of a mechanism for integrating persistent neural activity over time.

Color-specific conditioning effects due to both orange and blue stimuli are observed in a Halobacterium salinarum strain devoid of putative methylatable sites on HtrI.

Behavioral responses of Halobacterium salinarum appear as changes in the frequency of motion reversals. Turning on orange light decreases the reversal frequency, whereas blue light induces reversals. Light pulses normally induce the same response as step-up stimuli. However, anomalous behavioral reactions, including inverse responses, are seen when stimuli are applied in sequence. The occurrence of a prior stimulus is conditioning for successive stimulation on a time scale of the same order of adaptational processes. These prolonged conditioning effects are color-specific. The only adaptation process identified so far is methylation of the transducers, and this could be somehow color-specific. Therefore we tested for the behavioral anomalies in a mutant in which all methylation sites on the transducer have been eliminated. The results show that behavioral anomalies are unaffected by the absence of methylation processes on the transducer.

Phasic visual alertness in Alzheimer's disease and ageing.

An individual's ability to see and react quickly to a target stimulus is enhanced if they are alerted to the arrival of this target by a stimulus that occurs just prior in time to it. This alerting effect is thought to occur due to a phasic increase in alertness mediated by noradrenergic activity. In Alzheimer's disease (AD) there is a dysfunction in the noradrenergic system resulting in a decrease in central levels of noradrenaline. We therefore predicted that patients with AD would not be able to benefit from the prior stimulus to the same extent as that seen in healthy older adults and thus would have a reduced or abolished alerting-effect. We measured reaction times to respond to a visual target that could be preceded (by 200 ms) by a visual alerting cue, in 17 patients with Alzheimer's disease, 19 age-matched controls and 13 younger controls. We found that the alerting cue significantly decreased the reaction times for both the young and old controls, but that this cue had no effect upon the reaction times for those with AD. This marked inability to increase phasic alertness in AD may contribute to the everyday problems faced by these patients, and may provide a simple tool to aid diagnosis and disease progression.

Strength of prior stimuli determines the magnitude of secondary responsiveness in CD8+ T cells

CD8+T cells can become anergic following activation, though the cellular mechanism, as compared to CD4+ T cells, remains poorly understood. Here, we examined the effects of different antigen-dose, peptide ligands, and engagement of costimulatory molecules on the induction of CD8+ T cell anergy. We observed that increasing strengths of signals delivered to CD8+ T cells by varying the antigen-dose and the nature of peptide ligands induced increasing degrees of non-responsiveness to secondary stimulation. Furthermore, higher levels of LFA-3 engagement of CD2 rendered CD8+ T cells unresponsive to secondary antigenic re-challenge. This pattern of secondary responsiveness lasted up to 2 weeks following primary stimulation and was not correlated with prior cell division history. These results indicate that the strength of prior stimuli, which is determined by the sum of signals from both TCR and costimulatory molecules, determines the activation threshold and magnitude of CD8+ T cell responses.