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Biomedical subjects

I H Iversen

Publications and source records attributed to I H Iversen.

13 recordsLinked to original sources
PubMed2001

Self-initiation of EEG-based communication in paralyzed patients.

OBJECTIVES: Severely paralyzed patients could learn to voluntarily generate slow cortical potential (SCP) shifts in their electroencephalogram and to use these signals to operate a communication device. To enhance the patients' autonomy, the present study describes the development of a permanently available communication system that can be turned on and off by locked-in patients without external assistance. A skill necessary for turning the system on is the ability to regulate one's slow potentials in the absence of continuous feedback. METHODS: A stepwise learning approach was employed to train two paralyzed patients to regulate their SCPs without continuous feedback. Elements of the original communication system were gradually removed and elements of the new stand-by mode were introduced. RESULTS: At the end of the learning procedure, both patients achieved correct response rates of above 84% in training sessions without continuous feedback. This skill enabled them to turn the communication device on and off without assistance from others. CONCLUSIONS: These findings suggest that severely paralyzed individuals can learn to operate an EEG-based communication device autonomously.

Adult↗
PubMed1998

Simple and conditional visual discrimination with wheel running as reinforcement in rats.

Three experiments explored whether access to wheel running is sufficient as reinforcement to establish and maintain simple and conditional visual discriminations in nondeprived rats. In Experiment 1, 2 rats learned to press a lit key to produce access to running; responding was virtually absent when the key was dark, but latencies to respond were longer than for customary food and water reinforcers. Increases in the intertrial interval did not improve the discrimination performance. In Experiment 2, 3 rats acquired a go-left/go-right discrimination with a trial-initiating response and reached an accuracy that exceeded 80%; when two keys showed a steady light, pressing the left key produced access to running whereas pressing the right key produced access to running when both keys showed blinking light. Latencies to respond to the lights shortened when the trial-initiation response was introduced and became much shorter than in Experiment 1. In Experiment 3, 1 rat acquired a conditional discrimination task (matching to sample) with steady versus blinking lights at an accuracy exceeding 80%. A trial-initiation response allowed self-paced trials as in Experiment 2. When the rat was exposed to the task for 19 successive 24-hr periods with access to food and water, the discrimination performance settled in a typical circadian pattern and peak accuracy exceeded 90%. When the trial-initiation response was under extinction, without access to running, the circadian activity pattern determined the time of spontaneous recovery. The experiments demonstrate that wheel-running reinforcement can be used to establish and maintain simple and conditional visual discriminations in nondeprived rats.

Animals↗
PubMed1993

An experimental acquisition of maladaptive behavior by shaping.

In an attempt to demonstrate possible maladaptive effects resulting from shaping, two Long Evans rats were trained to jump onto a platform, then to extend their noses downward over the edge to a point where, losing their balance, they fell. The results showed how behaviors such as reaching and rearing can be reinforced differentially to bring about completely maladaptive behavior.

Animals↗
PubMed1993

Acquisition of matching-to-sample performance in rats using visual stimuli on nose keys.

Steady and blinking white lights were projected on three nose keys arranged horizontally on one wall. The procedure was a conditional discrimination with a sample stimulus presented on the middle key and comparison stimuli on the side keys. Three rats acquired simultaneous "identity matching." Accuracy reached 80% in about 25 sessions and 90% or higher after about 50 sessions. Acquisition progressed through several stages of repeated errors, alteration between comparison keys from trial to trial, preference of specific keys or stimuli, and a gradual lengthening of strings of consecutive trials with correct responses. An analysis of the acquisition curves for individual trial configurations indicated that the matching-to-sample performance possibly consisted of separate discriminations.

Animals↗
PubMed1993

Techniques for establishing schedules with wheel running as reinforcement in rats.

In three experiments, access to wheel running was contingent on lever pressing. In each experiment, the duration of access to running was reduced gradually to 4, 5, or 6 s, and the schedule parameters were expanded gradually. The sessions lasted 2 hr. In Experiment 1, a fixed-ratio 20 schedule controlled a typical break-and-run pattern of lever pressing that was maintained throughout the session for 3 rats. In Experiment 2, a fixed-interval schedule of 6 min maintained lever pressing throughout the session for 3 rats, and for 1 rat, the rate of lever pressing was positively accelerated between reinforcements. In Experiment 3, a variable-ratio schedule of 20 or 35 was in effect and maintained lever pressing at a very stable pace throughout the session for 2 of 3 rats; for 1 rat, lever pressing was maintained at an irregular rate. When the session duration was extended to successive 24-hr periods, with food and water accessible in Experiment 3, lever pressing settled into a periodic pattern occurring at a high rate at approximately the same time each day. In each experiment, the rats that developed the highest local rates of running during wheel access also maintained the most stable and highest rates of lever pressing.

Animals↗
PubMed1988

A multipurpose vertical holeboard with automated recording of spatial and temporal response patterns for rodents.

A method is presented for manual or automated recording of rats' spontaneous nose-poking ('visit') behaviors to a vertical holeboard with a matrix of 45 or 54 holes. Several behavior parameters are presented: visit frequency, visit duration, temporal visit pattern, spatial visit pattern, stereotype of visits, diversity of visits and variability of visit patterns. The paper describes the development of the apparatus and some methods of analyzing and presenting the multi-parametric data. The use of the apparatus is illustrated with a one-trial appetitive conditioning task. After 5 min in a single 10-min session, a food pellet is presented, only once in a given hole, to provide reinforcement of a spontaneous visit to that hole. The behavior parameters are compared before and after reinforcement. When the one-trial conditioning effect was challenged with d-amphetamine, the behavior parameters changed in a graded manner depending upon the dose (0.25-6.0 mg/kg). The apparatus has also proven useful for studies of exploratory behavior without using food reinforcement following lesion or drug interventions.

Animals↗
PubMed1987

Neostriatal lesions impaired rats' delayed alternation performance in a T-maze but not in a two-key operant chamber.

Rats with lesions in the neostriatal region that belongs to the prefrontal system were trained in two versions of delayed alternation. They performed as proficiently as intact animals in a two-key operant chamber. The same operated rats took many more trials to reach criterion when subsequently compared with the same control group in a T-maze. This finding demonstrates that variants of delayed alternation are not equivalent for animals with lesions in the prefrontal system. Observations suggested that delayed alternation in the operant chamber may be mastered by positional mediation.

Animals↗
PubMed1986

Stimulus definition in conditional discriminations.

With a customary arrangement of three horizontally aligned stimulus/response keys, two rhesus monkeys learned conditional hue and line discriminations--an "identity-matching" procedure. First, sample stimuli were presented on the center key, and comparison stimuli were presented on the two side keys. Next, the sample was allowed to appear on any one of the three keys, with the comparisons on the remaining two. The change from fixed to variable sample and comparison locations caused the horizontal and vertical lines to lose control over the animals' responses; the conditional hue discrimination remained intact. Accurate description of controlling stimuli in a matching-to-sample procedure may therefore require that their spatial location be specified.

Animals↗
PubMed1984

Discriminative control of hyperdipsic drinking in the baboon.

A baboon subject was surgically prepared with an arterial catheter and subsequently trained to elevate diastolic blood pressure with an operant schedule of food procurement and shock avoidance with associated discriminative stimuli. Blood pressure elevations developed in accordance with the requirements of the conditioning procedure. In addition, large-scale increases in water intake occurred on days when the conditioning sessions were in effect. Both blood pressure and water intake elevations were maintained when the conditioning procedure was changed to eliminate food reinforcement. Electrical monitoring of water spout contacts revealed that drinking occurred exclusively during response-produced SDS associated with food delivery, and did not occur either during response-produced SDS associated with electric shock, or during intertrial intervals. Because acute elevations in blood pressure preceded licking bouts, the drinking was not producing the pressor episodes. Overall, the data illustrate that drinking can occur in a systematic manner under the control of exteroceptive discriminative stimuli during non-skeletal response contingencies.

Animals↗
PubMed1984

Operant conditioning of autogrooming in vervet monkeys: Cercopithecus aethiops.

Vervet monkeys received food reinforcement contingent on autogrooming. Experiment 1 reinforced grooming on a schedule of increasing intermittency and grooming increased in frequency and duration; with only pauses reinforced, grooming decreased in frequency and duration. Experiment 2 demonstrated differentiation of operant autogrooming; in each session a different single form of grooming was reinforced (for example, grooming the tail only), and that form increased in frequency while other forms became less frequent. In Experiment 3 scratching was succesfully conditioned with a method that selectively reinforced variety in behavior; reinforcement was contingent on a shift in scratching form. In Experiment 4, with no contingencies on grooming, a prefood stimulus did not increase autogrooming whether or not grooming had previously resulted in contingent reinforcement. The form of conditioned autogrooming resembled the form of unconditioned autogrooming. The discussion suggests how reinforcement principles can account for changes in the topography of operant behavior.

Journal Article↗