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PubMed1989

Stimulus class formation and concept learning: establishment of within- and between-set generalization and transitive relationships via conditional discrimination procedures.

Three students with moderate mental retardation were taught a complex stimulus class with a two-choice conditional discrimination procedure applied across eight 10-member stimulus sets. Each set was composed of five age-appropriate and five age-inappropriate examples of clothing, accessories, and leisure items (e.g., a Walkman radio). Discrimination training was programmed serially across each set, and generalization probes were conducted concurrently among all sets. Generalization probes consisted of unreinforced conditional matching trials with comparison items being drawn from (a) the set undergoing training (within-set probes), (b) sets not undergoing training (between-set probes), and (c) both sample and comparison items from different sets (transitive stimulus control probes). Results indicate that within-set generalization, between-set generalization, and transitive stimulus relations controlled responding by all 3 students for items that had been contingently associated with reinforcement. However, items that gained control of responding through within-set and between-set generalization alone (i.e., not acquired through contingent reinforcement) remained at baseline levels during transitive stimulus control probes. Results are discussed in terms of a taxonomy of multiple sources of stimulus control that underlie socially defined and maintained stimulus classes.

Adolescent↗
PubMed2001

Visual search in peripheral vision: learning effects and set-size dependence.

Feature search for a light bar with one orientation (or color) embedded in an array of bars with a very different orientation (or color) is quick, easy and independent of the number of array elements. In contrast, search for a conjunction target has a linear response time dependence on the number of distractors. Training can improve performance of both these tasks. We report that these properties may not be valid for eccentric stimulus presentation. In general, the two hemifields are not equally suited to search, and training is most effective in the weaker hemifield. In addition, the feature-search independence of set-size may not always be valid for stimulus arrays that are presented peripherally. Subjects were tested on orientation and color feature tasks, and on orientation-color conjunction search with 3 array sizes presented at fixation or eccentrically in the right or left hemifield. During a second testing session, improvement was so much greater for the non-preferred hemifield that sometimes the preference was switched. Surprisingly, preferred hemifield performance actually declined for some subjects. Thus, the hemifield preference effect seems related to competition, and perhaps an automatic attention-directing mechanism. We confirmed the central presentation set-size independence for feature search but found a great difference between large and small arrays when presentation was lateral. There are two sources of this array size effect: 1. Target eccentricity, demonstrated by comparing performance for different target locations with the same array size. 2. Target location uncertainty, seen by comparing performance for different size arrays when the target elements appeared at the same locations. Training also affected the array-size dependence, changing search performance from set-size dependent to independent or vice versa at the point of greatest training effect.

Adult↗
PubMed1995

Relationship between visual acuity and observation distance.

The visual acuities of 17 young emmetropes and corrected ametropes were measured over the range of 7.5-0.19 m using a Bailey-Lovie chart. Accommodation stimulus-response measures were also taken over this range using retinoscopy to establish whether variations in visual acuity with observation distance could be attributed to accommodation behaviour. Tonic accommodation was recorded using the Canon R1 autorefractor and was compared with visual acuity and stimulus-response results. In general, visual acuity was found to be dependent on stimulus distance, being significantly reduced for most observers for the closest targets. There were three categories of observer performance for visual acuity as a function of observation distance; one group showing no change in visual acuity with distance, a second showing a flat function for distances 7.55-0.5 m, and then a decrease in visual acuity for shorter distances; and a third category that showed a maximum visual acuity in the 1.2-1.6 m region. This behaviour was unrelated to individual stimulus-response characteristics and there was no significant relationship between tonic accommodation and the distance where acuity was best for the third category observers.

Accommodation, Ocular↗
PubMed1978

A comparison of nicotine and structurally related compounds as discriminative stimuli.

1 Of seven nicotine-like compounds tested as discriminative stimuli in the rat, only 3-pyridyl-methylpyrollidine (3-PMP) generalized to the stimulus effects of nicotine. 2 3-PMP caused equivalent nicotine-like responding at a dose (800 microgram/kg) approximately 4 times that used for the original nicotine discrimination (200 microgram/kg). The ED50 for 3-PMP was about 5 times that for nicotine. 3 Testing of the compounds as possible antagonists of the nicotine-elicited cue were negative. 4 The nicotine-like cue produced by an 800 microgram/kg injection of 3-PMP was effectively blocked by mecamylamine but not by hexamethonium or atropine. Thus, 3-PMP appears to produce generalization to the nicotine cue via action on central nicotinic-cholinoceptors as has been previously reported for the nicotine discriminative stimulus. 5 Mecamylamine blocked the stimulus-effects of 3-PMP (800 microgram/kg) and of nicotine (200 microgram/kg) with an ED50 of 0.32 and 0.20 microgram/kg respectively.

Animals↗
PubMed1993

Discriminative stimulus properties of cocaine in the rat using a two-choice discrete-trial avoidance paradigm.

The discriminative stimulus effects of cocaine were studied in rats trained to discriminate 10.0 mg/kg cocaine from vehicle in a shock avoidance paradigm. Rats used could discriminate 10.0 mg/kg cocaine from vehicle within an average of 20 sessions after the start of discrimination training. Cocaine produced dose-dependent stimulus effects at 1.0- to 10.0-mg/kg doses. Cocaine (10.0 mg/kg) generalized to the dopamine reuptake inhibitor 1-[2-[bis(4-fluorophenyl)methyoxy]ethyl]-4-(3-phenylpropyl)piperaz ine 2HCl (GBR 12909) (30.0 mg/kg), methamphetamine (0.3 mg/kg), apomorphine (0.3 mg/kg), and the D2 dopamine agonist quinpirole (0.1 mg/kg), but not to the D1 dopamine agonist SK&F38393 (3.0-30.0 mg/kg). 1-Phenyl-2,3,4,5-tetrahydro-[1H]-3-benzazepine-7,8-diol HCl (SK&F38393) (10.0 mg/kg) combined with several doses (1.0-10.0 mg/kg) of cocaine shifted the stimulus generalization curve for cocaine to the left. Haloperidol (0.1 and 0.3 mg/kg), the D1 dopamine antagonist 7-chloro-2,3,4,5-tetrahydro-3-methyl-phenyl-1-H-benzazepine-7-ol maleate (SCH23390) (0.01-0.3 mg/kg), and the D2 dopamine antagonist S(-)-sulpiride (20.0 and 40.0 mg/kg) only partially blocked the stimulus effects of cocaine. Haloperidol (0.3 mg/kg) combined with SCH23390 (0.03 mg/kg) completely blocked the stimulus effects of cocaine. In addition, haloperidol (0.3 mg/kg) blocked the stimulus effects of quinpirole (0.1 mg/kg), in common with cocaine. These data suggest that both D1 and D2 dopamine receptors contribute to the discriminative stimulus effects of cocaine.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1990

Tolerance to morphine stimulus control: role of morphine maintenance dose.

Experiments assessed the development of tolerance to morphine stimulus control during treatment with selected maintenance doses of morphine. Separate groups of rats were trained to discriminate saline and either 3.2 mg/kg or 5.6 mg/kg morphine under fixed-ratio schedules of food delivery. Dose-response functions for generalization of morphine stimulus control were determined before, during, and after repeated treatment with selected doses of morphine. Similar experiments were performed with repeated pentobarbital treatment in order to assess the pharmacological selectivity of tolerance. Repeated treatment with saline, 3.2 mg/kg morphine, or twice daily injections of 17.8 mg/kg pentobarbital produced no tolerance to morphine stimulus control. In contrast, treatment with daily injections of 10 mg/kg or twice daily injections of 10 or 17.8 mg/kg morphine produced a dose-dependent increase in the dose of morphine required for stimulus control. The magnitude of tolerance to morphine stimulus control varied directly with the maintenance dose of morphine and was slightly greater for a lower than a higher morphine training dose. Termination of repeated treatment was followed by a return to initial sensitivity, without additional training. Tolerance to morphine stimulus control was not necessarily accompanied by tolerance to its rate-suppressing effects.

Animals↗
PubMed1978

The influence of stimulus velocity on the responses of single neurones in the striate cortex.

1. Using a multi-histogram technique forty-seven response-velocity curves were prepared for a variety of visual stimuli presented to twenty-one cells in the striate cortex of the anaesthetized, paralysed cat. 2. The character of each velocity-response curve varied according to the measurement used in assessing a response. Reasons are advanced for sampling the response over a single bin of short duration at the peak of the discharge in each average response histogram. 3. The sharpness of tuning varied markedly throughout the population of cells but it was not possible to establish any definitive class differences. 4. For simple and complex cell categories there was considerable overlap in both the range of effective stimulus velocities and the distribution of the optimal velocities. An observation not emphasized in the past was that some simple cells responded to very fast stimuli while a number of complex cells were driven by very slowly moving stimuli. 5. Generally changes in stimulus parameters such as the polarity of contrast of a moving edge, its orientation or direction of movement produced only slight modifications in the profile of the velocity-response curve. 6. The abolition of the response of simple cells that failed to be driven by rapidly moving stimuli was shown to be due to the entry of the stimulus into the inhibitory flank distal to the discharge region. When the movement of the stimulus was confined to the discharge region there was little evidence of velocity dependence in the response. The duration over which the inhibition from the distal flank remained effective was evaluated for representative simple cells.

Action Potentials↗
PubMed2004

Tolerance to the discriminative stimulus effects of ethanol following chronic inhalation exposure to ethanol in C57BL/6J mice.

A significant consequence of chronic ethanol (EtOH) exposure is the development of tolerance. The present study was designed to investigate tolerance to the discriminative stimulus properties of EtOH following chronic EtOH exposure. Adult male C57BL/6J mice were trained to discriminate EtOH (1.00 g/kg; i.p.) from saline, using a food-reinforced two-lever operant task. Following acquisition and establishment of criterion discrimination performance, a series of generalization tests were conducted to generate a baseline EtOH dose-response curve with a calculated ED50 dose of 0.42 g/kg. Mice were then placed into control (air) or EtOH inhalation chambers for 64 h. In Experiment 1, discriminative stimulus generalization tests with the EtOH ED50 dose conducted 24 h following chronic EtOH (or air) exposure did not yield significantly different EtOH responding, although a trend towards reduced sensitivity to the EtOH cue (tolerance) was evident. In Experiment 2, a cumulative dosing procedure (ED50=0.37 g/kg) was employed, yielding a baseline EtOH dose-response function with a calculated ED50 dose of 0.37 g/kg. At 24 h following chronic EtOH exposure, re-determination of the EtOH dose-response curve revealed a significant shift to the right, with more than a twofold increase in the ED50 value (ED50=1.09 g/kg) compared to the control air exposure condition (ED50=0.49 g/kg). This apparent tolerance to the EtOH cue dissipated in chronic EtOH-exposed mice tested 48 h following the inhalation treatment (ED50=0.51 g/kg). These results demonstrate tolerance to the discriminative stimulus effects of EtOH in C57BL/6J mice following chronic EtOH exposure in inhalation chambers.

Animals↗
PubMed1997

Reduction in excitability of the auditory nerve following electrical stimulation at high stimulus rates. II. Comparison of fixed amplitude with amplitude modulated stimuli.

We have previously shown that acute electrical stimulation of the auditory nerve using charge-balanced biphasic current pulses presented continuously can lead to a prolonged decrement in auditory nerve excitability (Tykocinski et al., Hear. Res. 88 (1995), 124-142). This work also demonstrated a reduction in electrically evoked auditory brainstem response (EABR) amplitude decrement when using an otherwise equivalent pulse train with a 50% duty cycle. In the present study we have extended this work in order to compare the effects of electrical stimulation using both fixed amplitude electrical pulse trains and amplitude modulated (AM) pulse trains that more accurately model the dynamic stimulus paradigms used in cochlear implants. EABRs were recorded from guinea pigs following acute stimulation using AM trains of charge-balanced biphasic current pulses. The extent of stimulus-induced reductions in the EABR were compared with our previous results using either fixed amplitude continuous, or 50% duty cycle pulse trains operating at 0.34 microC/phase (2 mA, 170 micros/phase) at 400 or 1000 pulses/s (Tykocinski et al., Hear. Res. 88 (1995) 124-142). The AM pulse train, operating at the same rates, was based on a 1-s sequence of the most extensively activated electrode of a Nucleus Mini-22 cochlear implant using the SPEAK speech processing strategy exposed to 4-talker babble, and delivered the same total charge as the fixed amplitude 50% duty cycle pulse train. Two hours of continuous stimulation induced a significant, rate-dependent reduction in auditory nerve excitability, and showed only a slight post-stimulus recovery for monitoring periods of up to 6 hours. Following 2 or 4 h of stimulation using an otherwise equivalent pulse train with a 50% duty cycle or the AM pulse train, significantly less reduction in the EABR was observed, and recovery to pre-stimulus levels was generally rapid and complete. These differences in the extent of the recovery between the continuous waveform and both the 50% duty cycle and AM waveforms were statistically significant for both 400 and 1000 pulses/s stimuli. Consistent with our previous results, the stimulus changes observed using AM pulse trains were rate dependent, with higher rate stimuli evoking more extensive stimulus-induced changes. The present findings show that while stimulus-induced reductions in neural excitability are dependent on the extent of stimulus-induced neuronal activity, the use of an AM stimulus paradigm further reduces post-stimulus neural fatigue.

Animals↗
PubMed1999

Differential involvement of dopamine in mediating the discriminative stimulus effects of low and high doses of caffeine in rats.

The hypothesis that low and high doses of caffeine produce effects that are differentially mediated by dopamine (DA) receptor mechanisms was investigated in rats trained to discriminate either 10 or 56 mg/kg of caffeine from saline. Rats trained to discriminate 56 mg/kg of caffeine acquired the discrimination in an average of 74 sessions, whereas rats trained to discriminate 10 mg/kg of caffeine required an average of 108 sessions. The DA D1 receptor agonist SKF 81297 and the DA D2 receptor agonist R(-)-propylnorapomorphine (NPA) generalized partially (50-75%) in rats trained to discriminate 10 mg/kg of caffeine, but produced predominantly saline-appropriate responding (< 40%) in rats trained to discriminate 56 mg/kg of caffeine. When SKF 81297 and NPA were combined, stimulus generalization was no greater than it was when either agonist was tested alone. The DA uptake inhibitors cocaine and GBR 12909 produced predominantly saline-appropriate responding in both groups of rats. Neither the DA D1 receptors antagonists SCH 23390 and SCH 31966, nor the DA D2 receptor antagonists eticlopride and sulpiride, generalized in rats trained to discriminate 10 or 56 mg/kg of caffeine. When administered in combination with caffeine, both the DA D1 and DA D2 antagonists antagonized completely the discriminative stimulus effects of the low training dose of caffeine, but did not alter the discriminative stimulus effects of the high training dose. These results suggest that the discriminative stimulus effects of 10 mg/kg of caffeine, but not 56 mg/kg of caffeine, are dependent on, but not limited to, DA D1 and D2 receptor mechanisms.

Animals↗
PubMed2006

Orientation response of haematophagous bugs to CO2: the effect of the temporal structure of the stimulus.

Carbon dioxide is generally recognized as an important cue used by haematophagous insects to locate a food source. When the mammalian hosts of these insects breathe, they normally emanate considerable amounts of CO2 at discrete intervals, i.e. with each exhalation. In this work, we analysed the effect of temporally pulsing CO2 on the host-seeking behaviour of Triatoma infestans. We investigated the ability of T. infestans to follow continuous and intermittent air pulses of 0.25, 0.5 and 1 Hz that included different concentrations of CO2. We found that insects were attracted to pulsed airstreams of 0.25 and 0.5 Hz transporting 400 ppm of CO2 above the ambient levels and to continuous streams added with the same amount of CO2. On the other hand, insects walked away from streams pulsed at rates of 1 Hz regardless of the amount of CO2 they bear. The walking trajectories displayed by bugs to attractive CO2-pulsed streams were as rectilinear and accurate as those to CO2-continuous streams. Our results are discussed in the frame of the interaction between olfactory and mechanoreceptive inputs as affecting the behavioural response of bugs.

Animals↗
PubMed2006

Imaging hair cell transduction at the speed of sound: dynamic behavior of mammalian stereocilia.

The cochlea contains two types of sensory cells, the inner and outer hair cells. Sound-evoked deflection of outer hair cell stereocilia leads to fast force production that will enhance auditory sensitivity up to 1,000-fold. In contrast, inner hair cells are thought to have a purely receptive function. Deflection of their stereocilia produces receptor potentials, transmitter release, and action potentials in the auditory nerve. Here, we describe a method for rapid confocal imaging. The method was used to image stereocilia during simultaneous sound stimulation in an in vitro preparation of the guinea pig cochlea. We show that inner hair cell stereocilia move because they interact with the fluid surrounding the hair bundles, but stereocilia deflection occurs at a different phase of the stimulus than is generally expected. In outer hair cells, stereocilia deflections were approximately 1/3 of the reticular lamina displacement. Smaller deflections were found in inner hair cells. The ratio between stereocilia deflection and reticular lamina displacement is important for auditory function, because it determines the stimulus applied to transduction channels. The low ratio measured here suggests that amplification of hair-bundle movements may be necessary in vivo to preserve transduction fidelity at low stimulus levels. In the case of the inner hair cells, this finding would represent a departure from traditional views on their function.

Animals↗
PubMed1986

Effects of stimulus mode on the acquisition, transfer, and generalization of categories by severely mentally retarded children and adolescents.

The effects of object training and photograph training on comprehension of category labels by severely mentally retarded children were explored. Relatively simple tasks (acquisition of trained examples and transfer between modes) and relatively difficult tasks (generalization to novel examples in the training mode and in the other mode) were both included. Results indicated that acquisition and transfer did not differ, yet generalization was significantly more accurate with objects than with photographs. Furthermore, generalization was significantly above chance for objects but not for photographs. Results were discussed in reference to discriminability between the two modes and possible constraints of decision-making demands on generalization performance.

Adult↗
PubMed2006

Determinants of range effects in face recognition.

The effects of test stimulus range on generalization gradients in humans were assessed for discriminations between faces that varied in brightness, faces that varied in orientation in the picture plane, and morphed faces. In Experiment 1, significant range effects, predicted by adaptation level theory, occurred when faces varied along the brightness or orientation dimension, but not for morphed faces. Changing the difficulty of discrimination of both training and test stimuli for Experiment 2 produced range effects in morphed faces. Experiment 3 explored training and testing stimulus factors as determinants of range effects in morphed faces. The results suggest that sufficiently biased testing ranges create shifts in response distributions (generalization gradients), and this may be amplified byusing relatively difficult discriminations between training stimuli.

Discrimination, Psychological↗
PubMed2002

Effects of ethanol on an acetaldehyde drug discrimination with a conditioned taste aversion procedure.

The current study was designed to investigate whether ethanol shares stimulus properties with acetaldehyde with the use of a discriminative taste aversion procedure. Animals were trained to discriminate a dose of acetaldehyde (0.2 or 0.3 g/kg, i.p.) from saline in eight consecutive cycles consisting of a pairing day (PD) and three nonpairing days (NPDs). On PDs, all animals were injected with a particular dose of acetaldehyde 30 min before a 20-min limited access to a saccharin solution [0.1% (wt./vol.)] and then injected immediately with either LiCl (0.15 M, 1.8 mEq) or saline. On the three following NPDs, animals were injected with saline and 30 min later were presented with the same saccharin solution for 20 min. All animals in each acetaldehyde training dose group acquired discriminative stimulus control before generalization tests were conducted. Results of generalization tests (ethanol doses of 0.8, 1.2, 1.6, and 2.0 g/kg) revealed that ethanol substituted for acetaldehyde at doses of 1.2 and 1.6 g/kg for both training doses of acetaldehyde. The findings for this study indicate that acetaldehyde and ethanol may share some stimulus properties.

Acetaldehyde↗