Stimulus coding rules for perceptual learning

Perceptual learning of visual features occurs when multiple stimuli are presented in a fixed sequence (temporal patterning), but not when they are presented in random order (roving). This points to the need for proper stimulus coding in order for learning of multiple stimuli to occur. We examined the stimulus coding rules for learning with multiple stimuli. Our results demonstrate that: (1) stimulus rhythm is necessary for temporal patterning to take effect during practice; (2) learning consolidation is subject to disruption by roving up to 4 h after each practice session; (3) importantly, after completion of temporal-patterned learning, performance is undisrupted by extended roving training; (4) roving is ineffective if each stimulus is presented for five or more consecutive trials; and (5) roving is also ineffective if each stimulus has a distinct identity. We propose that for multi-stimulus learning to occur, the brain needs to conceptually “tag” each stimulus, in order to switch attention to the appropriate perceptual template. Stimulus temporal patterning assists in tagging stimuli and switching attention through its rhythmic stimulus sequence.     

Stimulus concordance and risk-assessment in hermit crabs (Coenobita clypeatus): implications for attention

Recent research has demonstrated that the topography of defensive reactions depends on factors that are extraneous to the stimulus that elicits the defensive response. For example, hermit crabs will withdraw more slowly to the approach of a simulated visual predator (i.e., the eliciting stimulus) when in the presence of a coincident acoustic stimulus. Multiple properties related to the magnitude (e.g., duration, amplitude) of the acoustic stimulus have been found to modulate the crabs' withdrawal response (Chan et al., 2010b). We demonstrate that the proximity in spatial location between a threatening visual stimulus and a potentially distracting extraneous auditory stimulus is an important determinant of anti-predator behavior in hermit crabs. We suggest that a distal relationship between the eliciting stimulus and an unrelated signal may produce greater distraction. This marks the first reported experimental evidence of this relationship in an invertebrate species.     

Effects of cue information on response production and inhibition measured by event-related potentials

The aim of this study was to investigate how information carried by a cue stimulus modulate event-related potentials (ERPs) to a subsequent target stimulus which either calls for an overt response (Go stimulus) or no response (Nogo stimulus). One of the cues predicted the likely appearance of the Go stimulus (Go cue) whereas the other cue predicted the likely appearance of the Nogo stimulus (Nogo cue). Our results showed that unpredicted Nogo stimuli elicited enlarged N200 component. This finding supports the notion that Nogo N200 reflects response inhibition processes, i.e., the amplitude of the N200 is a function of the difficulty of response inhibition. In other words, increased N200 to Nogo stimuli following Go cues might be related to increased efforts in activating the response inhibition system thereby interrupting preparations to respond.     

Unconditioned Stimulus Revaluation to Promote Conditioned Fear Extinction in the Memory Reconsolidation Window

The retrieval-extinction paradigm, which disrupts the reconsolidation of fear memories in humans, is a non-invasive technique that can be used to prevent the return of fear in humans. In the present study, unconditioned stimulus revaluation was applied in the retrieval-extinction paradigm to investigate its promotion of conditioned fear extinction in the memory reconsolidation window after participants acquired conditioned fear. This experiment comprised three stages (acquisition, unconditioned stimulus revaluation, retrieval-extinction) and three methods for indexing fear (unconditioned stimulus expectancy, skin conductance response, conditioned stimulus pleasure rating). After the acquisition phase, we decreased the intensity of the unconditioned stimulus in one group (devaluation) and maintained constant for the other group (control). The results indicated that both groups exhibited similar levels of unconditioned stimulus expectancy, but the devaluation group had significantly smaller skin conductance responses and exhibited a growth in conditioned stimulus + pleasure. Thus, our findings indicate unconditioned stimulus revaluation effectively promoted the extinction of conditioned fear within the memory reconsolidation window.     

An arousing, musically enhanced bird song stimulus mediates circadian rhythm phase advances in dim light

A musically enhanced bird song stimulus presented in the early subjective night phase delays human circadian rhythms. This study determined the phase-shifting effects of the same stimulus in the early subjective day. Eleven subjects (ages 18-63 yr; mean +/- SD: 28.0 +/- 16.6 yr) completed two 4-day laboratory sessions in constant dim light (<20 lux). They received two consecutive presentations of either a 2-h musically enhanced bird song or control stimulus from 0600 to 0800 on the second and third mornings while awake. The 4-day sessions employing either the stimulus or control were counterbalanced. Core body temperature (CBT) was collected throughout the study, and salivary melatonin was obtained every 30 min from 1900 to 2330 on the baseline and poststimulus/postcontrol nights. Dim light melatonin onset and CBT minimum circadian phase before and after stimulus or control presentation was assessed. The musically enhanced bird song stimulus produced significantly larger phase advances of the circadian melatonin (mean +/- SD: 0.87 +/- 0.36 vs. 0.24 +/- 0.22 h) and CBT (1.08 +/- 0.50 vs. 0.43 +/- 0.37 h) rhythms than the control. The stimulus also decreased fatigue and total mood disturbance, suggesting arousing effects. This study shows that a musically enhanced bird song stimulus presented during the early subjective day phase advances circadian rhythms. However, it remains unclear whether the phase shifts are due directly to effects of the stimulus on the clock or are arousal- or dim light-mediated effects. This nonphotic stimulus mediates circadian resynchronization in either the phase advance or delay direction.     

Fractal Gait Patterns Are Retained after Entrainment to a Fractal Stimulus

Previous work has shown that fractal patterns in gait can be altered by entraining to a fractal stimulus. However, little is understood about how long those patterns are retained or which factors may influence stronger entrainment or retention. In experiment one, participants walked on a treadmill for 45 continuous minutes, which was separated into three phases. The first 15 minutes (pre-synchronization phase) consisted of walking without a fractal stimulus, the second 15 minutes consisted of walking while entraining to a fractal visual stimulus (synchronization phase), and the last 15 minutes (post-synchronization phase) consisted of walking without the stimulus to determine if the patterns adopted from the stimulus were retained. Fractal gait patterns were strengthened during the synchronization phase and were retained in the post-synchronization phase. In experiment two, similar methods were used to compare a continuous fractal stimulus to a discrete fractal stimulus to determine which stimulus type led to more persistent fractal gait patterns in the synchronization and post-synchronization (i.e., retention) phases. Both stimulus types led to equally persistent patterns in the synchronization phase, but only the discrete fractal stimulus led to retention of the patterns. The results add to the growing body of literature showing that fractal gait patterns can be manipulated in a predictable manner. Further, our results add to the literature by showing that the newly adopted gait patterns are retained for up to 15 minutes after entrainment and showed that a discrete visual stimulus is a better method to influence retention.     

‘Communication’ in weakly electric fish, Gnathonemus niger (Mormyridae) I. Variation of electric organ discharge (EOD) frequency elicited by controlled electric stimuli

The weakly electric fish, Gathonemus niger, discharged with a frequency of 4 to 8 Hz during the day and 10 to 16 Hz during the night. The frequency of superimposed burst discharges (32 to 56 Hz) was independent of diurnal factors. The variation of the electric organ discharge frequency during the day was investigated in response to controlled electric stimulus patterns: (a) A free running stimulus frequency of 4 Hz, simulating the resting frequency of another fish, and different stimulus intensities, simulating different distances between two fish. (b) Free running frequencies of 4, 8, 16, …, 128 Hz and two particular stimulus intensities. (c) Discharge coupled stimuli (each discharge triggered an electric stimulus with a fixed delay) and different stimulus intensities.All three kinds of stimuli elicited defined and predictable response discharge patterns supporting the assumption that an electric fish would respond to a particular discharge pattern of another fish also in a similar and predictable manner. Low stimulus intensities (0·04 to 0·2 mV per cm) caused cessation of the discharge activity, a ‘hiding’ or ‘listening’ response. The discharge rate increased linearly with the logarithm of the stimulus intensity. The fish was particularly sensitive to stimulus frequencies which simulated its burst activity (32 to 56 Hz). Discharge coupled stimuli showed that the fish responded to about eight times lower stimulus intensities if the stimulus occurred between two discharges (15 to 30 m-s after the fish's discharge) than if the stimulus occurred within or immediately after the discharge. All suprathreshold stimuli elicited a typical discharge pattern: The irregular resting discharge activity became significantly regular. The degree of regularity was even improved during maintained stimulation. The regularisation of the discharge activity is thought to be involved in the fish's electrolocating system whereas frequency variations are considered as being involved in both the locating system and as communication signals among weakly electric fish.     

Comparison of the mechanisms of latency shift in pattern reversal visual evoked potential induced by blurring and contrast reduction

Reduction of visual acuity or of the contrast of the stimulus induces a prolongation of the pattern reversal visual evoked potential (PR-VEP) latencies, perhaps because these conditions cause deterioration of the visual capacity to recognize objects and may preferentially activate the slower central retina channel. The PR-VEP was obtained with a video stimulator and 3 kinds of stimuli: total video field, video with a central scotoma and a restricted central stimulus. The subjects were tested under conditions of normal (20/20) and reduced visual acuity (20/200) with 14′ and 56′ checks and 60% contrast, and under conditions of normal visual acuity (20/20) with 14′ checks and with stimulus contrast of 60% and 25%. Blurring increased latencies and decreased amplitudes only with the 14′ checks stimulus but no with 56′ checks, and the amplitudes obtained with the central stimulus became greater than those obtained with a central scotoma. Reducing contrast increased only latency, and there was not difference between amplitudes obtained with a central stimulus or a central scotoma. We conclude that blurring small checks induces a preferential stimulation of receptors in the central retina, but the same effect was not observed when stimulus contrast was reduced.     

Opioid-like discriminative stimulus properties of benzomorphans in the pigeon: stereospecificity and differential substitution patterns

Pigeons were trained to discriminate the kappa-opioid agonist bremazocine (BREM) or the mu-opioid agonist fentanyl (FENT) from water. During tests of stimulus substitution, FENT and BREM failed to substitute for each other. The (-)-isomers of cyclazocine, pentazocine and ketocyclazocine substituted for the FENT but not the BREM stimulus. The (+)-isomers of these compounds, as well as the isomers of nallylnormetazocine, failed to substitute for either the FENT or BREM stimulus. In FENT- and BREM-trained pigeons, the (-)-isomers of cyclazocine, pentazocine, nallylnormetazocine and ketocyclazocine were more potent than their respective(+)-isomers in decreasing rates of responding. These results indicate that in the pigeon there is an isomeric separation of the discriminative stimulus properties of cyclazocine, pentazocine and ketocyclazocine and that the FENT-like stimulus effects of these drugs reside in their (-)-isomers. In addition, the present findings establish further that the classification of the discriminative stimulus effects of mu and kappa opioid compounds in the pigeon differ from those in rat and monkey.     

Contextual conditioning. A comparison of eastern and western views

Eastern and Western interpretations of contextual control of phasic conditional responses (transswitching) are contrasted. The Eastern (Asratyan, 1965) approach emphasizes the role of the tonic conditional stimulus and the (hypothetical) tonic response it evokes. The Western (Lachnit, 1986) approach emphasizes the role of compound conditional stimuli. Although Lachnit showed that transswitching-like results can be obtained without a tonic stimulus, attempts to simulate transswitching experiments using a computer model of the Rescorla-Wagner theory (Kimmel and Lachnit, 1988) have shown that predictions from the theory approximate empirical results in human classical conditioning only when the tonic stimulus is given far greater weight than the phasic stimulus. In other words, only when the Rescorla-Wagner theory is made more like Asratyan's theory, can the compound conditional stimulus approach account for real empirical transswitching data.     

Hippocampal State-Dependent Behavioral Reflex to an Identical Sensory Input in Rats

We examined the local field potential of the hippocampus to monitor brain states during a conditional discrimination task, in order to elucidate the relationship between ongoing brain states and a conditioned motor reflex. Five 10-week-old Wistar/ST male rats underwent a serial feature positive conditional discrimination task in eyeblink conditioning using a preceding light stimulus as a conditional cue for reinforced trials. In this task, a 2-s light stimulus signaled that the following 350-ms tone (conditioned stimulus) was reinforced with a co-terminating 100-ms periorbital electrical shock. The interval between the end of conditional cue and the onset of the conditioned stimulus was 4±1 s. The conditioned stimulus was not reinforced when the light was not presented. Animals successfully utilized the light stimulus as a conditional cue to drive differential responses to the identical conditioned stimulus. We found that presentation of the conditional cue elicited hippocampal theta oscillations, which persisted during the interval of conditional cue and the conditioned stimulus. Moreover, expression of the conditioned response to the tone (conditioned stimulus) was correlated with the appearance of theta oscillations immediately before the conditioned stimulus. These data support hippocampal involvement in the network underlying a conditional discrimination task in eyeblink conditioning. They also suggest that the preceding hippocampal activity can determine information processing of the tone stimulus in the cerebellum and its associated circuits.     

The influence of rate of temperature change and peak stimulus duration on pain intensity and quality

An important aspect of experimental pain research is that the assessment methods can investigate the different aspects of pain perception. The aim of the present study was to investigate the influence of rate of temperature change and peak stimulus duration on heat evoked pain intensity and quality. All stimuli were applied within the medial aspect of the anterior forearm. The rate of temperature change was varied from 1 to 16 C/s without any effect on the pain threshold. The pain threshold decreased with an increasing peak stimulus duration from 0.1 to 2 s, but not from 2 to 3 s. The pain intensity for suprathreshold stimuli (46 C, 48 C, 50 C) increased for decreasing rates and increasing duration. The pain intensity was highly correlated with the energy of the stimulus. When the rates of temperature change (1-16 C/s) are varied, no differences between pricking and burning pain were present at either low stimulus intensity (46 C) or high stimulus intensity (50 C). At low stimulus intensity (46 C), the pricking pain was not influenced by the duration (0.1-3 s), but the burning pain was intensified when the duration was increased from 1.5 to 3 s. At high intensity stimuli (50 C), the pricking pain intensified with an increased duration, whereas burning pain did not. The heat pain threshold is influenced by the peak stimulus duration, and not by the rate of temperature change. If suprathreshold stimuli are used, both the rate of temperature change and the peak stimulus duration can strongly affect the pain intensity and the pain quality. Therefore, the same stimulus modality can be used to assess the modulation of different pain intensities and of the pricking and burning pain qualities simply by varying the stimulus configuration.     

Postactivation potentiation in professional rugby players: optimal recovery

Following a bout of high-intensity exercise of short duration (preload stimulus), the muscle is in both a fatigued and a potentiated (referred to as postactivation potentiation) state. Consequently, subsequent muscle performance depends on the balance between these 2 factors. To date, there is no uniform agreement about the optimal recovery required between the preload stimulus and subsequent muscle performance to gain optimal performance benefits. The aim of the present study was to determine the optimal recovery time required to observe enhanced muscle performance following the preload stimulus. Twenty-three professional rugby players (13 senior international players) performed 7 countermovement jumps (CMJs) and 7 ballistic bench throws at the following time points after a preload stimulus (3 repetition maximum [3RM]): baseline, approximately 15 seconds, and 4, 8, 12, 16, and 20 minutes. Their peak power output (PPO) was determined at each time point. Statistical analyses revealed a significant decrease in PPO for both the upper (856 +/- 121 W vs. 816 +/- 121 W, p < 0.001) and the lower (4,568 +/- 509 W vs. 4,430 +/- 495 W, p = 0.005) body when the explosive activity was performed approximately 15 seconds after the preload stimulus. However, when 12 minutes was allowed between the preload stimulus and the CMJ and ballistic bench throws, PPO was increased by 8.0 +/- 8.0% and 5.3 +/- 4.5%, respectively. Based on the above results, we conclude that muscle performance (e.g., power) can be significantly enhanced following a bout of heavy exercise (preload stimulus) in both the upper and the lower body, provided that adequate recovery (8-12 minutes) is given between the preload stimulus and the explosive activity.     

The role of stimulus movement patterns in the prey catching behavior ofHydromantes genei (Amphibia,Plethodontidae)

Summary The prey catching responses of the Italian salamanderHydromantes genei (Schlegel) were studied both with respect to continuous stimulus movement and to stepwise stimulus movement. The stimulus consisted of a black square measuring 4×4 mm. The responses to both continuous and stepwise stimulus movement were measured at 3 different basic velocities (0.5, 1.25, and 3.125 cm/s), and to stepwise stimulus movement at 6 different step frequencies (0.25, 0.5, 1, 2, 4, 8 steps/s). The experiments showed that within the measured step frequency range, frequencies of 1 and/or 2 steps/s have proved to be the most efficient in eliciting prey catching behavior. The efficiency of both stepwise and continuous stimulus movement increases with an increase of the basic velocity, but the efficiency ratios of stepwise and continuous stimulus movement have an inverse relationship to each other: at low basic velocities, where continuous stimulus movement is less effective, stepwise stimulus movement of the same basic velocity is considerably more effective; at high basic velocities, where continuous stimulus movement is rather effective, the stepwise stimulus movement of the same basic velocity is either not significantly different or proves to be less effective.     

Integrated mismatch negativity (MMNi): a noise-free representation of evoked responses allowing single-point distribution-free statistical tests

If the repeated presentation of a single (standard) auditory stimulus is randomly interspersed with a second acoustically different (deviant) stimulus, the cortical activity evoked by the deviant stimulus can contain a negative component known as the mismatch negativity (MMN). The MMN is derived by subtracting the averaged response evoked by the standard stimulus from that evoked by the deviant stimulus. When the magnitude of the response is small or the signal-to-noise ratio is poor, it is difficult to judge the presence or absence of the MMN simply by visual inspection, and statistical detection techniques become necessary. A method of analysis is proposed to quantify the magnitude and statistically evaluate the presence of the MMN based on time-integrated evoked responses. This paper demonstrates the use of this integrated mismatch negativity (MMN_i) analysis to detect the MMN evoked by stimulus contrasts near the perceptual threshold of two subjects. The MMN_i, by virtue of being equivalent to a low-pass filtered response, presents an almost noise-free estimate of MMN magnitude. A single measure of the integrated evoked response at a fixed time point is used in a distribution-free statistic that compares the magnitude of the averaged response evoked by the deviant stimulus with a magnitude distribution derived from 200 subaveraged responses to the standard stimulus (with the number of sweeps per average equal to that of the deviant stimulus). This allows a calculation of the exact probability for the null hypothesis that the negative magnitude of the response evoked by the deviant stimulus is drawn from the magnitude distribution of responses evoked by the standard stimulus. Rejection of this hypothesis provides objective evidence of the presence of the MMN.     

Mechanics of Coriolis stimulus and inducing factors of motion sickness.

To specify inducing factors of motion sickness comprised in Coriolis stimulus, or cross-coupled rotation, the sensation of rotation derived from the semicircular canal system during and after Coriolis stimulus under a variety of stimulus conditions, was estimated by an approach from mechanics with giving minimal hypotheses and simplifications on the semicircular canal system and the sensory nervous system. By solving an equation of motion of the endolymph during Coriolis stimulus, rotating angle of the endolymph was obtained, and the sensation of rotation derived from each semicircular canal was estimated. Then the sensation derived from the whole semicircular canal system was particularly considered in two cases of a single Coriolis stimulus and cyclic Coriolis stimuli. The magnitude and the direction of sensation of rotation were shown to depend on an angular velocity of body rotation and a rotating angle of head movement (amplitude of head oscillation when cyclic Coriolis stimuli) irrespective of initial angle (center angle) of the head relative to the vertical axis. The present mechanical analysis of Coriolis stimulus led a suggestion that the severity of nausea evoked by Coriolis stimulus is proportional to the effective value of the sensation of rotation caused by the Coriolis stimulus.     

Startle responding and context conditioning. Naloxone pretreatment and stimulus intensity

The possibility that acoustic startle stimuli could support a conditional response (freezing) to contextual stimuli was investigated. Rats were exposed to three acoustic startle stimuli on the first day, and one on the second day. On day 1, 20 rats received naloxone pretreatment and another 20 received saline (placebo) pretreatment. Half of each group received a high-intensity acoustic stimulus, the other half a low-intensity acoustic stimulus. Both the higher stimulus intensity and the naloxone pretreatment led to greater freezing behavior during the 3-minute test period before the single startle stimulus on day 2. These findings support the notion that increased actual or perceived intensity of the acoustic startle stimulus increases conditioning to contextual stimuli as indexed by freezing behavior.     

Indicators of Early and Late Processing Reveal the Importance of Within-Trial-Time for Theories of Associative Learning

In four human learning experiments (Pavlovian skin conductance, causal learning, speeded classification task), we evaluated several associative learning theories that assume either an elemental (modified unique cue model and Harris’ model) or a configural (Pearce’s configural theory and an extension of it) form of stimulus processing. The experiments used two modified patterning problems (A/B/C+, AB/BC/AC+ vs. ABC-; A+, BC+ vs. ABC-). Pearce’s configural theory successfully predicted all of our data reflecting early stimulus processing, while the predictions of the elemental theories were in accord with all of our data reflecting later stages of stimulus processing. Our results suggest that the form of stimulus representation depends on the amount of time available for stimulus processing. Our findings highlight the necessity to investigate stimulus processing during conditioning on a finer time scale than usually done in contemporary research.     

Effective stage in the cell cycle for control of the budding direction of cdc mutants of Saccharomyces cerevisiae using electric stimulus

Cell division cycle (cdc) mutants of Saccharomyces cerevisiae were used to determine the most effective stage for the directional control of cell budding using an electric stimulus. The selected mutants were cdc 35 and cdc 28, which could be reversibly arrested before spindle pole body satellite formation (SPBSF) and spindle pole body duplication (SPBD), respectively. The budding direction (theta) was defined so that the direction parallel to that of the electric field was 0 degree. Considering the symmetry of the experimental conditions, the range of theta was defined as 0-90 degrees. The electric stimulus applied in the present study was alternating pulses (pulse height, +/- 15 V; pulse width at half pulse height, 5 microseconds; frequency; 10 kHz). The peak height of the cross membrane potential was estimated as 472 mV, which was sufficient to induce considerable strain in the cell membrane. In the case of cdc 35, the 95% confidence interval (95% CI) of the budding direction was 7-25 degrees when subjected to electric stimulus, while the 95% CI of the budding direction without electric stimulus was 35-57 degrees. In the case of cdc 28, 95% CI values of the budding direction with and without electric stimulus were 1229 degrees and 23-56 degrees, respectively. These results demonstrate that the stage after SPBD is effective for the directional control of yeast cell budding using an electric stimulus. Simultaneously, an electric stimulus reduced the cell budding time of both the cdc mutants used. Therefore, the electric stimulus was also effective in promoting cell cycle progression under the present conditions.