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PubMed2004

The aftereffects of ventriloquism: generalization across sound-frequencies.

Exposure to synchronous but spatially discordant auditory and visual inputs produces, beyond immediate cross-modal biases, adaptive recalibrations of the respective localization processes that manifest themselves in aftereffects. Such recalibrations probably play an important role in maintaining the coherence of spatial representations across the various spatial senses. The present study is part of a research program focused on the way recalibrations generalize to stimulus values different from those used for adaptation. Considering the case of sound frequency, we recently found that, in contradiction with an earlier report, auditory aftereffects generalize nearly entirely across two octaves. In this new experiment, participants were adapted to an 18 degrees auditory-visual discordance with either 400 or 6400 Hz tones, and their subsequent sound localization was tested across this whole four-octave frequency range. Substantial aftereffects, decreasing significantly with increasing difference between test and adapter frequency, were obtained at all combinations of adapter and test frequency. Implications of these results concerning the functional site at which visual recalibration of auditory localization might take place are discussed.

Adolescent↗
PubMed1997

[Two-stimulus--two choice paradigm for psychophysics: range-frequency model and adaptation level theory in comparison].

The predictions provided by the range-frequency model and the adaptation-level theory were compared in respect of size judgments in an averbal two-category experiment. Squares of different sizes were presented in two different frequency distributions. After a two stimulus-two choice training, in which the subjects (N = 64) learned to which of the two response categories a relative small or large square belonged, a generalization context-series test followed. The two test series represented the two different frequency distributions used (the arithmetic mean was either smaller or larger than the median or midpoint). The percentage of large responses was registered. Furthermore, to investigate which experimental design would be appropriate for this research paradigm, the study was carried out using both a between-subjects and a within-subjects design. For the two experimental designs, the results pointed to a confirmation of the predictions provided by the adaptation-level theory (D. R. Thomas, 1993) but not the range-frequency model (Parducci, 1983, 1995).

Adult↗
PubMed1997

Abrupt learning and retinal size specificity in illusory-contour perception.

BACKGROUND: In behavioral studies of learning, a distinction is commonly made between gradual and abrupt improvements in performance. The learning of perceptual and motor skills is often characterized by gradual, incremental improvement, and is found not to generalize over stimulus manipulations such as changes in the size or location of the retinal image. In contrast, marked improvement in performance can occur suddenly - a phenomenon which has been termed 'insight'. Consequently, the brain mechanisms subserving the two types of learning are commonly thought of as distinct. Here, we examine learning of a perceptual task in which improvement appears to exhibit characteristics of both gradual and abrupt learning. RESULTS: We describe experiments on illusory-contour perception in which the observers underwent an abrupt, dramatic improvement in performance, resembling an incident of insight. At the same time, however, the phenomenon showed a degree of stimulus-specificity that was previously thought to characterize incremental, gradual learning. The improvement was triggered only by specific visual stimuli, whereas other, quite similar, stimuli were found to be ineffective for training; the learning did not generalize to a new retinal image size, and re-training was necessary for different-sized images. CONCLUSIONS: The juxtaposition of abrupt and stimulus-specific learning that we observed suggests that the distinction between the two forms of learning needs to be revised. Rather than postulating two distinct mechanisms, incremental and insightful learning need to be addressed within a single framework. In particular, the findings suggest that learning may involve interactions between multiple levels of representations of the stimulus.

Adolescent↗
PubMed1995

P300 from auditory stimuli: intensity and frequency effects.

Auditory stimulus intensity (45, 60, 75 dB SPL) and standard/target frequency (250/500) and 1000/2000 Hz) were manipulated factorially to assess their effects on the P3(00) event-related brain potential (ERP). For the target stimuli, intensity increases produced reliable increases in P3 amplitude and decreases in peak latency. P3 latency at the lowest intensity level was marginally longer for the low frequency condition. For the standard stimuli, intensity increases produced reliable P3 amplitude increases, low frequency stimuli yielded smaller components than high frequency stimuli, and several interactions with the electrode factor were obtained. P3 latency decreased as intensity increased, and low frequency tones produced longer latencies than high frequency tones. The N1, P2, and N2 components from both stimulus types generally were affected in the same manner: intensity increases producing larger amplitudes and shorter latencies, with some effects of tone frequency also observed. The findings suggest that auditory stimulus parameters contribute to both P3 amplitude and latency measures in important ways and are discussed in relation to the use of ERPs in applied contexts.

Adult↗
PubMed1989

The influence of stimulus size on perimetric detection of small scotomata.

The influence of perimetric stimulus size on the detection of small scotomata was examined, and the blind spot was used as a paradigm of a small scotoma. A customized point pattern for perimetry was created on a Humphrey field analyzer. The point pattern had a density of 1.4 degrees and was arranged in a grid in the area of the blind spot. Four normal persons were tested with full-threshold strategy in the points of this grid using Goldmann stimulus sizes ranging from I to V. The delimitation of the blind spot was found to depend strongly on stimulus size. For small stimulus sizes, the blind spot could be delimited as an absolute scotoma with almost sharp borders. However, with larger spot sizes a relative scotoma zone gradually developed, extending centrally from the borders of the blind spot. The central absolute scotoma component of the blind spot totally disappeared for the largest stimulus sizes. We could establish that some of these larger stimuli would be projected totally within the optic nerve head, if perfect imaging through the refractive media of the eye, was assumed. We interpret our findings to be a result of light scattering in the refractive media of the eye, causing a blur to appear around the image of the light stimulus at the retinal plane. We conclude that perimetric resolution power is highly dependent on stimulus size. The smallest stimulus size possible should be used when dense stimulus patterns are used for perimetric detection of small scotomata.

Adult↗
PubMed1990

Magnesium-induced conditioned place preference in mice.

A conditioned place preference procedure was used in mice to test the hypothesis that magnesium possesses reinforcing properties. Mice were conditioned to the nonpreferred end of a three-compartment straight shuttle box with MgCl2 injections alternating with saline injections on the preferred end. Dose of MgCl2 was varied (0, 15, 30, 125 mg/kg) as well as number of conditioning trials (8 or 16). On the day after the first postconditioning test, animals were given acute injections of 5 mg/kg cocaine, or other test drug, to determine if the conditioned effect on behavior would be potentiated, maintained or blocked by these test drugs. Results demonstrated that 15 mg/kg MgCl2 induced the greatest amount of conditioning and that increasing the number of MgCl2/place pairings did not enhance the amount of conditioning, but rather, it decreased it. Amphetamine potentiated MgCl2-induced place preference; cocaine and pentobarbital maintained it; and haloperidol blocked it. These data indicate that MgCl2 has some primary reinforcing properties in mice and that MgCl2 shares stimulus properties with other stimulants and reinforcing substances.

Animals↗
PubMed1994

Discriminative stimulus properties of 7-OH-DPAT, a dopamine D3-selective receptor ligand.

7-Hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT) is a high affinity and selective ligand at dopamine D3 receptors. Rats were trained to discriminate 7-OH-DPAT (0.05 mg/kg) from drug vehicle using a food-reinforced (FR 10) two-lever operant procedure. Six out of nine rats learned to discriminate 7-OH-DPAT, requiring a mean of 29 training sessions. After the training dose was increased to 0.10 mg/kg the remaining three rats reached discrimination performance criterion. The 7-OH-DPAT stimulus was dose-dependent. Doses of 0.01, 0.03, 0.056, and 0.1 mg/kg 7-OH-DPAT produced 0, 11, 78, and 100% drug-correct lever selection, respectively, with the ED50 value calculated to be 0.038 mg/kg. These results demonstrate that the D3-selective ligand 7-OH-DPAT can control differential operant responding in rats on the basis of its discriminative stimulus properties.

Animals↗
PubMedDate not supplied

Effects of restraint stress and intra-ventral tegmental area injections of morphine and methyl naltrexone on the discriminative stimulus effects of heroin in the rat.

The effect of restraint stress on the discriminative stimulus properties of heroin and the role of the opioid receptor activation in the ventral tegmental area in heroin discrimination were examined. In Experiment 1, male rats were trained to discriminate heroin (0.5 mg/kg, SC) from saline under conditions of exposure to restraint (15 min/day; three times a week) or no stress. Dose-response curves were subsequently determined under conditions of no stress, restraint, corticosterone (3 mg/kg, IP), and saline. Exposure to restraint during training did not alter heroin discrimination under any of the conditions tested. In contrast, administration of restraint or the stress hormone corticosterone just prior to drug injections decreased sensitivity to the heroin cue. In Experiment 2, injections of morphine (5-10 micrograms/side) into the ventral tegmental area (VTA, the cell body region of the mesocorticolimbic dopamine neurons) did not result in heroin-appropriate responding in animals trained to discriminate heroin injected systemically from saline. Furthermore, intra-VTA injections of the opioid antagonist methyl naltrexone (0.75-3.0 micrograms/side) did not block the discriminability of heroin given systemically. These results indicate that exposure to restraint stress or the stress hormone corticosterone in close temporal contiguity to the drug injection may reduce the sensitivity to the opioid cue. In addition, under the condition of the present experiment activation of opioid receptors in the VTA does not appear to mimic the discriminative stimulus effects of systemically administered heroin.

Animals↗
PubMed1969

Tilted lines as complex stimuli.

Severely retarded boys were taught to respond differentially to lines tilted at 45 degrees and 135 degrees . While all subjects could perform the discrimination, the aspect of the stimulus that controlled responding was shown to differ among subjects.

Adolescent↗
PubMed1994

The metabolic consequences of an increase in the frequency of stimulation in isolated ferret hearts.

1. The metabolic consequences of an increase in the frequency of stimulation were examined in isolated ferret hearts. Intracellular pH (pHi) and the intracellular concentrations of phosphocreatine ([PCr]i), inorganic phosphate ([Pi]i) and ATP were measured by 31P nuclear magnetic resonance (NMR) spectroscopy. 2. Increasing the stimulus rate from 0.1-0.7 to 2 Hz caused an increase in [Pi]i and a decrease recovery of both [PCr]i and [Pi]i during continued stimulation. There was no change in [ATP]i during stimulation at 2 Hz. Increasing the stimulus rate caused an intracellular acidosis of around 0.1 pH units. 3. Increasing the stimulus rate generally caused an initial increase in developed pressure, followed by a decrease over 1-2 min to a steady level slightly lower than developed pressure at the low (control) stimulus rate. The increase in stimulus rate caused a 4- to 6-fold increase in time-averaged muscle activity. 4. Both oxygen uptake and production of lactate increased on 2 Hz stimulation. Lactate production accounted for less than 5% of ATP production at low or high stimulus rates, suggesting that significant anoxia was not occurring during stimulation. The observed lactate production was, however, sufficient to explain most of the intracellular acidosis observed when the stimulus rate was raised. When glycolysis was prevented by removal of glucose and depletion of glycogen stores, 2 Hz stimulation was accompanied by an intracellular alkalosis rather than an acidosis, suggesting that lactate production by glycolysis was the cause of the intracellular acidosis. 5. Reducing the rate of glycolysis increased the size of changes in [PCr]i and [Pi]i evoked by stimulation at 2 Hz. Furthermore, there was now no partial reversal of the changes in [PCr]i and [Pi]i during 2 Hz stimulation. 6. When oxidative phosphorylation was inhibited by replacing O2 with N2, increasing the rate of stimulation from 0.1-0.7 to 1-2 Hz caused an initial increase followed by a large fall in developed pressure, which declined to a level well below that at the control stimulus rate. The increase in stimulus rate was accompanied by a large fall in [PCr]i, an increase in [Pi]i, and an intracellular acidosis of 0.1-0.3 pH units. The fall in developed pressure was consistent with the known effects of the rise in [Pi]i and the fall in pHi on the contractile apparatus.

Adenosine Triphosphate↗
PubMed1980

[Functional change in the type of response of retinal ganglion cell receptive fields].

27% of 270 receptive fields of the ganglionic cells did not change their firing on alteration of intensity, duration or colour of the stimulus or general adaptation background. These "pure" off-receptive fields constituted the 4th group. The majority of the receptive fields, however, changed their type of firing on alteration of the stimulus parameters, and some of the fields revealed all three classes of responses: on-, on-off and off-. Three groups of receptive fields were distinguished on the ground of common regularities of functional readjustments. These findings render the Hertline classes overlapping and show the correctness of classification to depend on the experimental conditions.

Adaptation, Physiological↗
PubMed1986

Cannabidiol attenuates delta 9-tetrahydrocannabinol-like discriminative stimulus effects of cannabinol.

Interaction effects of cannabidiol (CBD) and cannabinol (CBN) were examined using a drug discrimination procedure in which rats had been trained to discriminate between 3 mg/kg of delta 9-tetrahydrocannabinol (delta 9-THC) and vehicle (2 ml/kg). The generalization effects of CBN to delta 9-THC were attenuated when CBN was administered together with CBD. The results were time- and dose-dependent.

Animals↗
PubMed1991

The discriminative stimulus effects of neuropeptide Y.

Neuropeptide Y (NPY), an endogenous peptide which strongly induces food intake, is demonstrated to have discriminative stimulus properties when administered intracerebroventricularly. Rats rapidly learned to press the appropriate lever during training. NPY discrimination was dose-dependent. NPY's discriminative stimulus properties were compared to those of two doses of Peptide YY (PYY) and 24 and 48 h of food deprivation, conditions which also increase feeding. Both doses of PYY generalized to NPY, supporting previous findings that PYY has effects similar to NPY. Although food deprivation increases feeding in a manner similar to NPY, food deprivation did not result in NPY-appropriate responding.

Animals↗
PubMedDate not supplied

Effects of vasopressin on the habituation of the orienting reaction in men.

Effects of arginine-vasopressin (AVP) on the habituation of the orienting reaction and response to stimulus mismatch were investigated in a between-group design with 40 healthy male volunteers using skin conductance and heart rate responses as dependent measures. Twenty-one 1000 Hz tones of 90 dB(A) intensity and 2 s duration were presented with alternating intervals of 20 and 140 s. Stimulus mismatch responses were analyzed to the tones after the long intervals and to a change of the interval duration. The expected prevention of habituation as an indicator of a general stimulus-related increase of phasic arousal under AVP could not be confirmed. There were no differences between the AVP and the placebo group in the skin conductance and heart rate responses. The interval change did not provoke a dishabituation reaction, but responses to the tones after the long intervals were reliably enhanced. However, AVP did not increase the reaction to stimulus mismatch. It is concluded that autonomic indicators of the habituation of the OR remain unaffected by AVP.

Acoustic Stimulation↗