Decrease In Discriminative Performance Research Articles

Idiographic duo–trio tests using a constant-reference based on preference of each consumer: Sample presentation sequence in difference test can be customized for individual consumers to reduce error

As reformulations and processing changes are increasingly needed in the food industry to produce healthier, more sustainable, and cost effective products while maintaining superior quality, reliable measurements of consumers' sensory perception and discrimination are becoming more critical. Consumer discrimination methods using a preferred-reference duo–trio test design have been shown to be effective in improving the discrimination performance by customizing sample presentation sequences. However, this design can add complexity to the discrimination task for some consumers, resulting in more errors in sensory discrimination. The objective of the present study was to investigate the effects of different types of test instructions using the preference-reference duo–trio test design where a paired-preference test is followed by 6 repeated preferred-reference duo–trio tests, in comparison to the analytical method using the balanced-reference duo–trio. Analyses of d' estimates (product-related measure) and probabilistic sensory discriminators in momentary numbers of subjects showing statistical significance (subject-related measure) revealed that only preferred-reference duo–trio test using affective reference-framing, either by providing no information about the reference or information on a previously preferred sample, improved the sensory discrimination more than the analytical method. No decrease in discrimination performance was observed with any type of instruction, confirming that consumers could handle the test methods. These results suggest that when repeated tests are feasible, using the affective discrimination method would be operationally more efficient as well as ecologically more reliable for measuring consumers' sensory discrimination ability.

On-line Identification of Seeds in Mandarins with Magnetic Resonance Imaging

Mandarins have been inspected using magnetic resonance imaging (MRI) in order to detect the presence of seeds. To enhance contrast between seeds and pulp, effective transverse relaxation time-weighted fast low angle shot images (703 ms acquisition time) were acquired. Stationary fruits were imaged and then the images were segmented to extract several features. The maximum radius of the region containing the seeds and the central axis rmax, and the perimeter of this region P were the most powerful features for discrimination between seedless and seed-containing fruits. Such features were the most robust since they showed the lowest noise-to-signal ratios (N/S). The proportions of correct classification were 88·9% and 86·7% for seedless and seed-containing fruits, respectively, under MRI stationary conditions. The performance under on-line conditions was evaluated by imaging the fruits while conveyed at 54 mm/s. An analysis of variance with the features extracted from the static images and the motion-corrected dynamic images showed that there were statistically indistinguishable. The proportions of correct classification were 92·5% and 79·5% for the seedless and seed-containing category, respectively, under MRI dynamic conditions. Reduction in the distance between categories for rmax was addressed as the main cause for the decrease in discrimination performance. The robustness of the motion correction procedure was highlighted by the low differences in the N/S ratio and the noise-to-measured range ratios between static and dynamic features.

Amplitude compression in cochlear implants artificially restricts the perception of temporal asymmetry.

This paper presents a study in which five cochlear implantees were asked to discriminate the timbre of stimuli with temporally asymmetric envelopes. Stimuli were damped and ramped sinusoids presented acoustically. They were transformed by the speech processor of the implant and were presented through one electrode. All cochlear implantees could discriminate the damped and ramped sinusoids when the half-life was 4 ms, the carrier frequency was 400 Hz, and the period of the envelope was 50 ms. In a second experiment, timbre discrimination performance was measured as a function of half-life for two cochlear implantees. Both showed that timbre discrimination was possible over the range 1-24 ms. In normal-hearing listeners, the range is 1-64 ms and in cochlear implantees, stimulated directly without the speech processor, the range is 1-300 ms. At long half-lives, the decrease in discrimination performance observed with the speech processor appears to be due to the amplitude compression applied by the device. The present results suggest that it may be important to ensure that cochlear implants do not restrict temporal asymmetry unduly when applying compression to control level.

Discriminative effects of cocaethylene in rats trained to discriminate cocaine or ethanol

Two groups of rats were trained to discriminate between the stimulus properties of either intraperitoneally administered 10.0 mg/kg cocaine or 600 mg/kg ethanol and its vehicle in a two-lever operant chamber. Once trained, both groups exhibited a dose-related decrease in discriminative performance when tested with lower doses. A dose of 10 mg/kg cocaine, as well as doses of 10–30 mg/kg cocaethylene, in the ethanol-trained animals produced no greater than 38.9% responding on the ethanol-appropriate lever. Combinations of the approximate ethanol ED 50 dose with either 10 mg/kg cocaine or 20 mg/kg cocaethylene did not increase ethanol lever responding. In contrast, in the cocaine-trained animals, administration of cocaethylene produced dose-responsive cocaine-like discrimination with 30 mg/kg producing 88.9% responding on the cocaine-appropriate lever. In addition, 600 mg/kg ethanol co-administered with a (2.5 mg/kg) dose of cocaine that was poorly discriminated produced 85% of responses on the cocaine-appropriate lever. The peak effect of cocaine and cocaethylene were observed to occur in 15–30 min post-administration with cocaine choice behavior decreasing at a faster rate than seen for cocaethylene discrimination. Results are discussed in light of ethanol and cocaine producing a heightened, as well as prolonged, euphoria in humans.

Cocaine discrimination is attenuated by isradipine and CGS 10746B

The discriminative stimulus properties of cocaine are thought to be mediated by dopaminergic mechanisms that may be modulated by calcium ion influx and/or interact with 5-hydroxytryptamine 3 (5-HT 3) receptors. To test these possibilities, rats were trained to discriminate between the stimulus properties of 10.0 mg/kg cocaine and its vehicle in a two-lever, food-motivated operant task. Once trained, rats showed a dose-related decrease in discriminative performance when tested with lower cocaine doses. An analysis of the dose-response curve indicated an ED 50 value of 3.04 mg/kg. Pretreatment with the presynaptic dopamine release-inhibiting agent CGS 10746B (20–40 mg/kg) resulted in a dose-related decrease in cocaine discrimination with the highest dose significantly attenuating cocaine discrimination. Pretreatment with 10–30 mg/kg isradipine, a calcium channel blocker, also resulted in a dose-related decrease in cocaine discriminative performance. In contrast to these positive results, pretreatment with the 5-HT 3 receptor antagonist MDL 72222 (3.5–7.0 mg/kg), or the same doses of ibogaine, did not significantly affect cocaine discrimination. The results suggest that cocaine controls differential responding in a discriminative stimulus task by mechanisms that involve presynaptic release of dopamine, which may be regulated by neuronal calcium influx through L-type calcium channels.

Effect of altering dopamine or serotonin neurotransmitters upon cathinone discrimination

Rats were trained to discriminate between the stimulus properties of 0.8 mg/kg l-cathinone and its vehicle in a two-lever, food-motivated operant task. Once trained, rats showed a dose-related decrease in discriminative performance when tested with lower cathinone doses. An analysis of the dose-response curve indicated an ED 50 value of 0.23 mg/kg. Pretreatment with CGS 10746B (5–20 mg/kg) resulted in a dose-related decrease in cathinone discrimination with the highest dose blocking cathinone discrimination. In contrast to the ability of this dopamine release inhibitor to decrease cathinone discrimination, pretreatment with three doses of the calcium channel blocker isradipine (2.5–10 mg/kg) or with the 5-HT 3 antagonist MDL 72222 (0.1–0.4 mg/kg) had no effect upon cathinone discrimination. The results suggest that cathinone controls differential responding in a discriminative stimulus task by a mechanism involving presynaptic release of dopamine, which may not be regulated by either neuronal calcium influx through L-type calcium channels or by serotonergic neurons.

Effect of serotonin depletion by p-chlorophenylalanine upon discriminative behaviours

1. 1. Para-chlorophenylalanine ( p-CPA), a competitive inhibitor of the serotonin (5-HT) synthesis enzyme tryptophan hydroxylase, was administered to rats at a dosage (100 mg/kg daily for 3 days) that depletes 5-HT. 2. 2. Different groups of these rats were previously trained to discriminate the interoceptive stimuli produced by amphetamine, cathinone, 3,4-methylenedioxymethamphetamine (MDMA), N-ethyl-3,4-methylenedioxyamphetamine (MDE), fenfluramine or yohimbine, and the effect of p-CPA pretreatment upon their discriminative performance was compared with the effect of saline (control) pretreatment. 3. 3. p-CPA was shown to have no effect upon the dopaminergically-mediated stimuli produced by the stimulants amphetamine and cathinone or upon yohimbine performance. 4. 4. p-CPA significantly decreased discriminative performance with the serotonergic releasing drugs MDMA, MDE and fenfluramine. This decrease in discriminative performance returned to pre- p-CPA (criterion) levels at a time (9–12 days) when 5-HT has been reported to replete to normal brain concentrations. 5. 5. It is concluded that p-CPA pretreatment lowers brain 5-HT and, in turn, significantly decreases the ability of rats to discriminate centrally active drugs whose interoceptive cueing stimuli are mediated by 5-HT neurons.

Discriminative stimulus properties of flesinoxan

Different groups of rats were trained to discriminate either 0.3 mg/kg of flesinoxan (N = 13) or 0.1 mg/kg of 8-OH-DPAT (N = 7) from saline in a two-lever operant drug discrimination task using a fixed ratio 10 schedule of reinforcement. Once trained, animals in both groups displayed a dose-related decrease in discriminative performance upon administration of lower doses of the drug used in training. In generalization tests, flesinoxan generalized to 8-OH-DPAT in 8-OH-DPAT-trained animals and 8-OH-DPAT substituted for flesinoxan in flesinoxan-trained animals. Buspirone substituted partially for both the flesinoxan and the 8-OH-DPAT cue. The results of the present study indicate similarity between the discriminative stimulus effects of flesinoxan and the stimulus produced by the 5-HT1A agonist 8-OH-DPAT. These results, coupled with the finding that flesinoxan has a significant affinity and selectivity for 5-HT1A binding sites, suggest that the stimulus effects of flesinoxan are mediated by a 5-HT1A mechanism.

Discriminative stimulus properties of flesinoxan

Different groups of rats were trained to discriminate either 0.3 mg/kg of flesinoxan (N=13) or 0.1 mg/kg of 8-OH-DPAT (N=7) from saline in a two-lever operant drug discrimination task using a fixed ratio 10 schedule of reinforcement. Once trained, animals in both groups displayed a dose-related decrease in discriminative performance upon administration of lower doses of the drug used in training. In generalization tests, flesinoxan generalized to 8-OH-DPAT in 8-OH-DPAT-trained animals and 8-OH-DPAT substituted for flesinoxan in flesinoxan-trained animals. Buspirone substituted partially for both the flesinoxan and the 8-OH-DPAT cue. The results of the present study indicate similarity between the discriminative stimulus effects of flesinoxan and the stimulus produced by the 5-HT 1A agonist 8-OH-DPAT. These results, coupled with the finding that flesinoxan has a significant affinity and selectivity for 5-HT 1A binding sites, suggest that the stimulus effects of flesinoxan are mediated by a 5-HT 1A mechanism.

MDMA as a discriminative stimulus: Isomeric comparisons

Using a two-lever, food-motivated discrimination procedure, eight male rats were trained to discriminate 1.5 mg/kg of racemic 3,4-methylenedioxymethamphetamine (MDMA) from its vehicle, distilled water. Once trained, the rats demonstrated a dose-related decrease in discriminative performance after administration of lower doses of MDMA (ED50=0.27 mg/kg). Racemic MDMA-stimulus generalization occurred with both isomers of MDMA with the ED50 of the (+) isomer calculated as 0.50 mg/kg and for the (−) isomer being 1.07. Time-course data indicate that racemic MDMA has a peak effect from 20–60 min post-injection with a declining effect from 120–140 min. This time-course closely resembles that observed by subjective reports in human abusers and, together with previous data, would indicate that the discriminative paradigm would be useful in investigations as to the neurochemical effects of MDMA.

Amfonelic acid: Similarity to other dopamine agonists

Rats were trained to discriminate between the stimulus properties of intraperitoneally administered 0.8 mg/kg amfonelic acid and its vehicle in a two-lever, food-motivated operated task. Once trained, rats showed a dose-related decrease in discriminative performance with lower amfonelic acid doses and analysis of the dose-response curve indicated an ED50 of 0.11 mg/kg. Administration of 0.08–0.6 mg/kg d-amphetamine produced a pattern of responding similar to that observed with amfonelic acid, with an ED50 of 0.10 mg/kg and a non-parallel dose-response curve. Likewise, the discriminative stimulus properties of amfonelic acid were shown to generalize to both d, l-cathinone and cocained but not to apomorphine. The results suggest that amfonelic acid, as well as other non-amphetamine stimulants, acts by a different mechanism of action than does amphetamine and biochemical studies are reviewed to further evidence this observation.

Discriminative stimulus properties of the serotonergic agent 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)

Using a two-lever drug discrimination procedure, six rats were trained to discriminate 0.5 mg/kg of racemic 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) from saline. Once trained, the animals demonstrated a dose-related decrease in discriminative performance upon administration of lower doses of DOI (ED50 = 0.16 mg/kg). DOI-stimulus generalization occured with the putative 5-HT 2 agonist DOM (ED50 = 0.49 mg/kg), but not with the 5-HT 1A agonist 8-OH DPAT, or the 5-HT 1B agonist TEMPP. Furthermore, the DOI stimulus could be antagonized by pretreatment of the animals with the 5-HT 2 antagonist ketanserin. The present results, coupled with the prior demonstration that DOI possesses a significant affinity and selectivity for 5-HT 2 binding sites, suggest that the discriminative stimulus effects of DOI may be 5-HT 2-mediated.

Discriminative properties of l-cathinone compared to dl- and d-cathinone

Rats were trained to discriminate between the stimulus properties of 0.6 mg/kg l-cathinone and its vehicle in a two-lever, food-motivated operant task. Once trained, rats showed a dose-dependent decrease in discrimination performance with lower l-cathinone doses and analysis of the dose-response relationship indicated an ED50 of 0.19 mg/kg. Administration of either dl- or d-cathinone produced a pattern of discriminative responding similar to l-cathinone with ED50s of 0.29 and 0.63 mg/kg, respectively. Thus, the potency of the racemeric cathinone lies approximately midway between that of the two isomers. Time-course data indicate that l-cathinone has a peak effect at 15–30 min post-administration with a duration of 180 min. Pretreatment with the serotonic receptor blocker pirenperone did not affect l-cathinone discrimination, whereas pretreatment with 0.2 mg/kg haloperidol, a dopamine receptor blocking agent, attenuated the l-cathinone discrimination. These data suggest that the stimulus properties of l-cathinone are possibly mediated by brain dopaminergic systems.

Effect of dopamine agonists and fenfluramine on discriminative behavior in obese and lean Zucker rats

Dopamine agonists and fenfluramine were used as pharmacological probes to investigate the possible difference in sensitivity and time course of drug action in genetically obese Zucker rats and their leatermates. All rats were trained to discriminate between the stimulus properties of 0.6 mg/kg d-amphetamine and its vehicle in a two-lever, food-motivated operant task. Once trained, both groups of rats showed a dose-related decrease in discriminative performance with lower amphetamine doses. Analysis of the dose-response curves indicated an ED50 for the obese rats of 0.17 mg/kg and for the lean group of 0.14 mg/kg. Administration of 0.3–1.2 mg/kg l-amphetamine and 2.5–10.0 mg/kg cocaine produced a pattern of responding similar to that observed with d-amphetamine. In contrast, 0.08-mg/kg apomorphine produced saline-appropriate responding and 1.5–2.5 mg/kg fenfluramine produced intermediate results in both groups. Time-course experiments indicated that the lean rats maintain errorless discriminative performance through 90 min post-injection, whereas the obese rats discriminate d-amphetamine significantly less at that post-administration time. The results susimilar sensitivity to d-amphetamine and other dopaminergic agonists in obese and lean rats with a difference in the time-course of d-amphetamine's action between these two groups.

Apomorphine increases ethanol discrimination

Rats were trained to discriminate between the stimulus properties of 600 mg/kg ethanol and saline in a two-lever, food-motivated operant task. Once trained, rats showed a dose-related decrease in discriminative performance with lower ethanol doses and analysis of the dose-response curve indicated an ED50 of 372 mg/kg. Pretreatment with 0.16 mg/kg apomorphine produced increased discriminative performance at each ethanol dose and the combination generated a dose-response curve parallel to ethanol administered alone with an ED50 of 232 mg/kg. This significant shift to the left of the ethanol dose-response curve after apomorphine administration is discussed in relation to dopaminergic neuronal systems and the clinical use of apomorphine in alcoholics.

Discriminative stimulus properties of the serotonin agonist 1-(3-trifluoromethylphenyl) piperazine (TFMPP)

Using a standard two-lever drug discrimination procedure, twelve rats were trained to discriminate 1.0 mg/kg of the serotonin (5-HT) agonist TFMPP from saline. Once trained, the animals displayed a dose-related decrease in discriminative performance upon administration of lower doses of TFMPP. Tests of stimulus generalization were performed using the purported 5-HT agonist RU-24,969 and 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). While TFMPP produced stimulus effects similar to those of RU-24,969, these effects seem to be dissimilar to those of DOM. The results of the present study suggest that the discriminative stimulus effects of TFMPP may involve a 5-HT 1-related mechanism.

Comparison of behavioral effects of cathinone, amphetamine and apomorphine

Rats were trained to discriminate between the stimulus properties of 0.6 mg/kg ±-cathinone and its vehicle in a two-lever, food-motivated operant task. Once trained, rats showed a dose-related decrease in discriminative performance with lower cathinone doses and analysis of the dose-response curve indicated an ED50 of 0.24 mg/kg. Administration of 0.2–0.8 mg/kg d-amphetamine produced a pattern of responding similar to that observed with cathinone. The dose-response curve after d-amphetamine was shown to be parallel to that of cathinone and the ED50 generated was 0.21 mg/kg. Thus, cathinone was equi-potent to d-amphetamine in this behavioral paradigm. In contrast, administration of 0.16–0.32 mg/kg apomorphine produced intermediate results. The results suggest a common site and/or mechanism for action of ±-cathinone and d-amphetamine.

Phenytoin: Similarity to tricyclic antidepressants

Rats were trained to discriminate between the stimulus properties of intraperitoneal injections of 10 mg/kg phenytoin and its pH-adjusted vehicle in a two-lever, food-motivated operant task. Once trained, rats showed a dose-related decrease in discriminative performance with lower phenytoin doses. Administration of pentobarbital and chlordiazepoxide produced vehicle-appropriate responding, whereas injection of imipramine and amitryptaline produced intermediate results. Desipramine, at an intraperitoneal dose of 10 mg/kg, produced a pattern of responding similar to that observed after the training dose of phenytoin. These results demonstrate, for the first time, the ability of a non-disruptive dose of phenytoin to act as a behavioral discriminative stimulus in the rat and suggest the possibility of a common interoceptive cue property with tricyclic antidepressants.