Reaction times identify a Pavlovian component in a two-choice discrimination

Six pigeons discriminated on discrete trials between two colors. In Experiment 1, two luminous spots were both either blue or green and the reinforced responses were “peck left” for blue and “peck right” for green. In Experiment 2, the hue of a center spot controlled subsequent choice pecks to left or right. In both experiments response bias was manipulated in two ways. During stimulus frequency (“SF”) sessions correct responses brought food on 40% of trials; in “imbalanced” blocks of sessions one hue appeared on 80% of trials and the other on 20%. During reinforcement probability (“RNF”) sessions the hues appeared equally often, but in imbalanced blocks the hues signaled different reinforcement probabilities, either 64% or 16%. In “balanced” control blocks the hues appeared equally often and were both reinforced at 40%. The experiments gave similar results. When bias was computed from choice percentages the imbalanced conditions yielded substantial response bias, and the amount of bias was about the same under RNF and SF treatments. However, reaction times (RTs) gave a different outcome. RNF imbalance slowed responses directed at the less reinforced stimulus, but SF imbalance had little RT effect (Experiment 1) or no effect (Experiment 2). These results suggest that choice was controlled by an instrumental stimulus-response-reinforcement association, whereas RTs were controlled by a Pavlovian stimulus-reinforcement association.     

The effect of intruded events on peak time: the role of reinforcement history during the intruded event

Pigeons were studied in an extension of a study by Aum et al. [Aum, S., Brown, B.L., Hemmes, N.S. 2004. The effects of concurrent task and gap events on peak time in the peak procedure. Behav. Process. 65, 43-56] on timing behavior under a discrete-trial fixed-interval (FI) procedure during which 6-s intruded events were superimposed on peak-interval (PI) test trials. In Aum et al., one event consisted in termination of the timing cue (gap trial); the other was a stimulus in the presence of which subjects had been trained to respond under an independent random-interval (RI) schedule of reinforcement (concurrent task trial). Aum et al. found a disruption of timing on concurrent task trials that was greater than that on gap trials. The present study investigated history of reinforcement associated with intruded events as a possible explanation of this earlier finding. After training to peck a side key on a 30-s PI procedure, discrimination training was conducted on the center key in separate sessions; red or green 6-s stimuli were associated with RI 24s or EXT (extinction) schedules. During testing under the PI procedure, three types of intruded events were presented during probe trials--the stimulus associated with the RI (S+) or EXT (S-) schedule during discrimination training, or a gap (termination of the side-keylight). Intruded events occurred 3, 9, or 15s after PI trial onset. Effects of reinforcement history were revealed as substantial disruption of timing during the S+ event and relatively little disruption during the S- event. Intermediate effects were found for the gap event. Results indicate that postcue effects are at least partially responsible for the disruptive effects of the S+ event.     

Performance of mice in an automated olfactometer: odor detection, discrimination and odor memory

Mice were trained on a variety of odor detection and discrimination tasks in 100- or 200-trial sessions using a go, no-go discrete trials operant conditioning procedure. Odors, presented for 1 s on each trial, were generated by an air dilution olfactometer (for threshold tests) and an easily constructed eight-channel liquid dilution unit (for two- and multiple-odor discrimination tasks). Mice rapidly acquired the operant task and demonstrated excellent stimulus control by odor vapors. Their absolute detection threshold for ethyl acetate was similar to that obtained with rats using similar methods. They readily acquired four separate two-odor discrimination tasks and continued to perform well when all eight odors were presented in random order in the same session and when reinforcement probability for correct responding was decreased from 1 to 0.5. Memory for these eight odors, assessed under extinction after a 32 day rest period, was essentially perfect. Time spent sampling the odor on S+ and S- trials was highly correlated with response accuracy. When accuracy was at chance levels (e.g. initial trials on a novel task), stimulus sampling time on both S+ and S- trials was approximately 0.5-0.7 s. As response accuracy increased, sampling time on S+ trials tended to increase and remain higher than sampling time on S- trials.     

Odor-sampling time of mice under different conditions

Response accuracy and odor sample times on positive (S+) and negative (S-) trials were recorded for mice trained on a variety of go, no-go odor detection and discrimination tasks. Odor sample time was relatively stable over extended training on the same task, increased during acquisition of difficult tasks, relatively insensitive to reinforcement magnitude, and, in some cases, provided more information regarding task difficulty and discrimination than did response accuracy. Mice generally sampled longer on S- trials in simple odor detection tasks but longer on S+ trials in odor discrimination tasks.     

Learning and discrimination of colored papers in jumping spiders (Araneae, Salticidae)

Color discrimination in jumping spiders Hasarius adansoni was examined by heat-avoidance learning in association with colored papers. The arena for the experiment was divided into two halves by a pair of colored papers. The colored papers used in this study were blue, green, yellow, red, white, gray and black. In training sessions, one half of the arena was heated from the bottom by a hot plate, and freely walking spiders were individually trained to avoid the heated half. In subsequent memory tests without heat, they consistently avoided the heat-associated colored papers. We found that jumping spiders could learn blue-green, blue-yellow, blue-red, blue-gray, green-yellow, green-red, green-gray, yellow-red, yellow-gray and red-gray patterns. Moreover, spiders trained with a blue-white pattern, a green-white pattern, a yellow-white pattern or a red-white pattern could discriminate the blue, green, yellow or red from black. It seems that jumping spiders can discriminate the blue, green, yellow and red papers by their hue, although brightness may also be used together with the color cue to discriminate colored papers.     

Wing Colour Properties do not Reflect Male Condition in the American Rubyspot (Hetaerina americana)

Adult males of the American rubyspot ( Hetaerina americana ) dispute riverine territories where females arrive to mate. On the wing basis, these males bear a red pigmentation spot whose area correlates with territorial disputes and mating rate: males with larger spots are more successful. This is explained by the fact that spot size correlates with fat muscular reserves which fuel flight during territorial intrusions. To further our understanding of sexual selection acting on the spot, here we have examined possible differences in three spot colour properties (red chroma, hue and brightness) in three distinct adult male ages [young, middle-aged (when males are more likely to defend a territory) and old], social status (territorial and non-territorial in middle-aged males), and under two potentially, energetically and costly situations: when faced with an immune challenge [comparing a nylon-implanted male group vs. a non-implanted male group in two ages, teneral (previous to colour formation) and middle-aged] and low diet levels (comparing a male set of middle-aged animals that received food ad libitum vs. a male set that received no food). Our results indicate no change in colour properties across any of these comparisons. Taken together, these and previous results suggest that only spot size but not the spot characteristics we measured here, is sexually selected in males of this species at least in terms of pre-copulatory male–male competition. That some of these colour properties have been related to male condition in other calopterygid damselflies cannot be generalized to the American rubyspot.     

A note on select- and reject-controlling relations in the simple discrimination of capuchin monkeys (Cebus apella)

Controlling relations in the simple discrimination performances of capuchin monkeys (Cebus apella) were studied in two experiments using a blank-comparison procedure. The main goal was to determine whether monkeys would (a) select an S+ stimulus if another stimulus was substituted for the S- (indicating a select-controlling relation) and (b) reject an S- if another stimulus was substituted for S+ (indicating a reject-controlling relation). In experiment 1, two simple simultaneous discriminations were established, one of which was reversed repeatedly until rapid reversal learning was exhibited. During subsequent probe tests, some behavior was consistent with select- and reject-controlling relations, but there was also substantial variability. To control the variability, the procedures of experiment 2 were designed to establish select- and reject-control relations directly by training with the blank-comparison procedure. On subsequent probe trials, new stimuli were substituted for the blank comparison. Both animals exhibited consistent, reliable select- and reject-controlling relations. These experiments are the first to employ the blank-comparison procedure with non-human subjects. They also demonstrate a reliable method for generating select- and reject-controlling relations for experimental study.     

Asymmetric suppression of components in binary aldehyde mixtures: behavioral studies in the laboratory rat

The aim of the present study was to assess component interaction in the perception of the 2 aldehydes butanal and heptanal when presented in binary mixtures to rats. A further aim was to develop a behavioral paradigm for testing suppression of components in mixtures using rodent subjects. Thirsty rats were initially trained to discriminate between the 2 aldehydes butanal and heptanal in an olfactometer using a go/no-go discrimination task. This involved rats learning to place their noses in a sniff port where odors were presented and to lick a tube for water reward when one of the aldehydes was presented (S+) while withholding licking at the tube to the other, unrewarded, aldehyde (S-). A mixture condition was then introduced into the task, whereby a proportion of trials involved presentation of a combination of the 2 aldehydes as an additional unrewarded condition. Rats readily learned to withhold licking on trials when the mixture was presented. The concentration of the nonrewarded (S-) aldehyde in the mixture was then systematically decreased, whereas the concentration of the S+ component was held constant. This eventually caused the S+ component in the mixture to suppress detection of the S-, as shown by an increasing number of lick responses (false alarms) on trials when the mixture was presented. These suppressing effects occurred well above the detection threshold for the S- aldehyde presented alone. Results showed asymmetric suppression in the mixture condition such that butanal suppressed detection of heptanal at much lower concentrations than vice versa. A second experiment showed that when both butanal and heptanal were present in a binary mixture at the same concentration (10(-6) volume %), then rats responded to the mixture as if only butanal was present. These findings are discussed in terms of butanal having higher mobility and being able to compete more effectively than heptanal for occupation of shared receptor sites.     

Genetic differentiation among populations and color variants of sea cucumbers (Stichopus japonicus) from Korea and China

The Far Eastern sea cucumber, Stichopus japonicus, is a favored food in Eastern Asia, including Korea, Japan, and China. Aquaculture production of this species has increased because of recent declines in natural stocks and government-operated stock release programs are ongoing. Therefore, the analyses of genetic structure in wild and hatchery populations are necessary to maintain the genetic diversity of this valuable marine resource. In addition, given that sea cucumber color affects market price, with the rare, possibly reproductively isolated, red type being the most valuable, an understanding of the genetic structure and diversity in color variation of green and red types is necessary. We analyzed the genetic structure of wild and hatchery-produced green type S. japonicus from Korea and China, and wild red type from Korea using 9 microsatellite makers. The number of alleles per locus ranged from 11 to 29 across all populations. The mean allele numbers of the green types from Korea (10.6) and China (10.1) were similar, but differed slightly from that of the red type (9.1). Pairwise multilocus F(ST) and genetic distance estimations showed no significant differences between the green types from Korea and China, whereas the differences between the green and red types were significant. This was clearly illustrated by a UPGMA dendrogram, in which the two close subclusters of green types were completely separated from the red type. In addition, the allele frequencies of the green and red types were significantly different. Assignment tests correctly assigned 100% (quality index 99.97%) of individuals to their original color types and demonstrated the feasibility of microsatellite analysis for discrimination between color types.     

Is the structural and psittacofulvin‐based coloration of wild burrowing parrots Cyanoliseus patagonus condition dependent?

The bright colours of parrots are caused by psittacofulvin pigments, which appear unique to this Order, and by structural colours. We measured red (psittacofulvin), green (mixed) and blue (structural) colours of wild burrowing parrots Cyanoliseus patagonus of northeastern Patagonia, Argentina, and measured nestlings regularly to obtain data on breeding success and nestling growth. As adult feathers are moulted outside the breeding season, adult body condition could not be measured directly during feather growth, and climatic conditions were used as an indirect parameter. The colony of burrowing parrots is surrounded by Monte steppe habitat, the breeding success has been shown to depend strongly on the climatic patterns. The area experienced a drought with very poor breeding success as well as a year of above‐average precipitation during the study period, serving as a natural experiment. We thus analysed the variability of colouration within the population among and within breeding seasons. We observed strong inter‐annual differences in nestling and adult colouration. Nestlings grew blue feathers with lower achromatic brightness during better conditions, and when controlling for year effects, nestlings with higher mass and from more successful families also had blue feathers with lower achromatic brightness. Adult blue feathers showed the same trend, with lower achromatic brightness in the moult following breeding seasons of better conditions. In contrast, during better conditions, adults grew red feathers with higher achromatic brightness and the colour hue was also affected, and the hue of the red region of nestlings varied with the hatching order. The colour of all three regions of nestlings varied between nests, and the colour of the red region of adult males positively correlated with breeding success (clutch size, brood size). In summary, the present data suggest that environmental conditions contribute to variability in both structural and the psittacofulvin‐based colours of wild burrowing parrots.     

Electrodermal discrimination with visual feedback in two incompatible stressful situations. A yoked control comparison

One group (N = 14) of human volunteers received three sessions of discriminated avoidance and punishment with the skin resistance response (SRR) as the instrumental behavior. Each session consisted of three 7 minute periods of Sidman avoidance (response-stimulus [R-S] and stimulus-stimulus [S-S] = 40 sec) of a 0.5 second, 15 Hz square wave shock mixed with three periods of punishment with the same shock. The avoidance and punishment periods were differentially signaled by red and green lights, and a circle appeared superimposed on the discriminative stimuli during a criterion SRR. A second group (N = 14) was yoked to the first by recording shock events on magnetic tape and shocking the yoked subject in the same temporal sequence. In both groups the visual feedback stimulus was consistently related to the subject's ongoing electrodermal behavior. As in previous research, the contingent shock subjects made significantly more SRRs during avoidance than during punishment in all three sessions. For yoked subjects the discrimination did not appear until the third session. The findings imply that the discrimination is at least partly independent of the avoidance and punishment contingencies, and they raise questions about the role of the feedback stimulus.     

Stimulus class formation and functional equivalence in moderately retarded individuals' conditional discrimination

Three mentally retarded humans first acquired a simple discrimination: Simultaneously displayed visual stimuli A1 and A2 functioned as S+ and S-, respectively. The subjects also acquired a conditional discrimination, learning to select visual stimuli B1 and B2 conditionally upon A1 and A2, respectively. Then, B1 and B2 were displayed without A1 or A2. Subjects selected B1, an emergent discrimination that showed that B1 and B2 had become functionally equivalent to A1 and A2, respectively. Two subjects next learned to select C1 and C2 conditionally upon B1 and B2, respectively. They also learned to select B1 and B2 conditionally upon D1 and D2, respectively. Subsequent simple discrimination probe trials displayed (a) C1 and C2 and (b) D1 and D2. On the former, the subjects nearly always selected C1. On the latter, they initially selected D1 and D2 about equally often. Thus, the emergence of simple discrimination appears to depend on a specific experimental history.     

Color discrimination in wild boars

Two experiments were carried out in order to clarify the color perception of Japanese wild boarsSus scrofa leucomystax. Two females were trained using an operant conditioning technique to press a switch under a positive stimulus color card in order to receive food as a reward. In Exp. 1, they were tested for discrimination between 3 colors (red, green and blue) and gray. The luminosity of all colors was the same. The wild boars succeeded in discrimination tests between blue and gray, but failed to discriminate red from gray. They also did not discriminate green from gray so clearly as blue from gray. In Exp. 2, the same wild boars were tested to discriminate between 8 kinds of color, which were created by gradating green yellow into red purple except for the 3 colors used in Exp. 1, and gray. They could clearly discriminate blue, purple blue and a part of purple from gray. In these experiments, wild boars were capable of recognizing bluish colors. However, for colors approaching green or yellow, they failed the test by degrees.     

Recognition of incomplete patterns by bumble bees

Bumble bees were trained to discriminate between two visual patterns, one of which was rewarding (S+) and one of which was unrewarding (S-). Subsequently, they were tested for discrimination between two non-rewarding patterns: the top halves of the training patterns, the bottom halves or the side halves. Three conditions were tested: (1) When the S+ was a star and the S- was a circle, all halves of the star were chosen above chance level, which may reflect an unlearned preference for radial patterns. (2) When the S+ and S- were reversed, the bottom half and the side half of the circle were chosen above chance level, but not the top half. (3) In the last condition, the S+ was again a circle, but the feeder tube was placed below the training pattern rather than above, and again the bottom halves were discriminated but neither the top nor the side halves were. In learning pattern discriminations, the ventral portion of the pattern is weighted more strongly than the dorsal portion, which enables recognition of incomplete patterns, and the weighting depends little on angle of approach.     

Similar effects of a beta-carboline and of flumazenil in negatively and positively reinforced learning tasks in mice.

Methyl beta-carboline-3-carboxylate (beta-CCM) and flumazenil (Ro15-1788) are known to be respectively an inverse agonist and an antagonist of the central benzodiazepine-receptor. Surprisingly, these two drugs have shown a similar enhancing effect in a negatively reinforced multiple-trial brightness discrimination task in mice. Thus, to evaluate the role of anxiety in this task, the action of these two drugs were compared in the same learning task with a positive or a negative reinforcement. Mice were trained for sessions of ten trials per day for six consecutive days. The sessions during the first three days took place after administration of beta-CCM (0.3 mg/kg), flumazenil (15 mg/kg) or vehicles of these drugs. A negative reinforcement (electric foot-shock) was used in a first experiment, and a positive one (food reward) in a second experiment. Results showed that, whatever the reinforcement, the two drugs enhance learning in a brightness discrimination task. The hypothesis is that flumazenil could have an inverse agonist profile in learning tasks. The question remains as to whether the flumazenil enhancing learning process results from increased arousal and/or anxiogenic factors, or from a negative modulatory influence of endogenous diazepam-like ligands for benzodiazepine receptors.     

Colour discrimination learning in black-handed tamarin (<Emphasis Type="Italic">Saguinus midas niger</Emphasis>)

Colour is one cue that monkeys use for perceptual segregation of targets and to identify food resources. For fruit-eating primates such as Saguinus, an accurate colour perception would be advantageous to help find ripe fruits at distance. The colour vision abilities of black-handed tamarins (Saguinus midas niger) were assessed through a discrimination learning paradigm using Munsell colour chips as stimuli. Pairs of chips were chosen from an early experiment with protan and deutan humans. The monkeys (three males and one female) were tested with stimuli of the same hue, but different brightness values, in order to make sure that discriminations were based on colour rather than brightness cues. The results showed that the female, but not the males, presented an above-chance performance for stimuli resembling hue conditions under which tamarins forage (oranges vs greens). Colour vision in S. m. niger is discussed according to the advantages and disadvantages of dichromatism in daily search for food as well as to aspects regarding polymorphism in New World monkeys.     

Olfactory discrimination of eight food flavors in the capuchin monkey (Cebus apella): Comparison between fruity and fishy odors

Operant conditioning was used to investigate how primates discriminate between odor qualities. Eight artificial food flavors, selected from either a “Fishy” or “Aroma/Fruity” category, were used. During the presence of one of the two odors S+ or S−, the monkey was reinforced by pushing a response key when S + was presented. The tufted capuchins discriminated most accurately when both odors were Aroma. Discrimination was more accurate when S+ was Fruity odor and S− was Fishy odor. When both odors were Fishy, discrimination could not be acquired in 20 sessions. All of the flavors used, except apple, were novel for the subjects, which suggests that capuchins can innately discriminate among them. The data also suggest that Aroma odors are more salient than Fishy odors. The results also suggested an innate aversion to Fishy odors.     

Enhanced contrast of bacteriophage plaques in Salmonella with ferric ammonium citrate and sodium thiosulfate (FACST) and tetrazolium red (TZR)

Visualization of bacteriophage plaques may be enhanced by addition of ferric ammonium citrate and sodium thiosulfate (FACST) or 2,3,5-triphenyltetrazolium chloride (tetrazolium red, TZR) to the soft agar layer of a traditional bacteriophage plaque assay. Background color from these reagents improved contrast between clear plaques and turbid host lawns in trypticase soy agar (TSA) plates. Enhancement by FACST is based on reaction with hydrogen sulfide gas (H2S) produced by some strains of bacteria and was tested here using H2S+ and H2S- strains of Salmonella enterica subsp. enterica with a bacteriophage (Podoviridae) isolated from swine lagoon effluent. Only the H2S+ strain produced dark brown-black color in FACST-amended agar. Both strains showed bright pinkish-red color in TZR-amended agar. Color intensity for both reagents decreased with decreasing concentrations of the reagents. Contrast in FACST-amended plates appeared greater than that with TZR, but diminished after 12 h, while contrast in TZR-amended plates remained constant. At the concentrations tested, neither reagent affected plaque counts in the H2S+ strain. The FACST should be useful in bacteriophage plaque assays with H2S+ strains of Salmonella and other H2S+ bacteria.     

Bending of z-lines by mechanical stimuli: an input signal for integrin dependent modulation of ion channels?

We studied which components of mechanical cell deformation are involved in "stretch modulated ion currents" (SMIC). Murine ventricular myocytes were attached to glass coverslips and deformed in x, y and z with a 16 microm thin glass stylus (S) of calibrated stiffness. Three-dimensional confocal microscopy characterized cell deformation (T-tubular membranes, mitochondria) and bending of S (indicative of the applied force). Axial (x-) displacement of S sheared the upper cell part versus the attached bottom, close to S, it changed sarcomere length and bent z-lines ("z-line displacement"). Vertical (z-press) or transversal (y-shear) displacement of S bulged cytoplasm and mitochondria transversally without detectable z-line displacement. Axial stiffness increased with the extent of stress ("stress stiffening"). Depolymerization of F-actin or block of integrin receptors reduced stiffness. SMIC served as a proxy readout of deformation-induced signaling. Axial deformation activated a non-selective cation conductance (Gns) and deactivated an inwardly rectifying K+ conductance (GK1), z-press or y-shear did not induce SMIC. Depolymerization of F-actin or block of integrin receptors reduced SMIC. SMIC did not depend on changes in sarcomere length but correlated with the extent of z-line bending. We discuss that both shear stress at the attached cell bottom and z-line bending could activate mechanosensors. Since SMIC was absent during deformations without z-line bending we postulate that z-line bending is a necessary component for SMIC signaling.     

A single laser method for subtraction of cell autofluorescence in flow cytometry

In flow cytometry cell autofluorescence often interferes with efforts to measure low levels of bound fluorescent antibody. We have developed a way to correct for autofluorescence on a cell-by-cell basis. This results in improved estimates of real staining and better separation of the fluorescence histograms of stained and non-stained cells. Using a single laser, two-color fluorescence measurement system and two-color compensation electronics, autofluorescence and one fluorescent reagent are measured (rather than two fluorescent reagents). With fluorescein-conjugated antibodies the signal in the 515 to 555 nm range (green fluorescence) includes both fluorescein emission and part of the cellular autofluorescence. In the cases we have investigated, autofluorescence collected at wavelengths above 580 nm ("red") is well correlated with the green autofluorescence of the cells. A fraction of this red fluorescence is subtracted from the green fluorescence to produce an adjusted fluorescein output on which unstained cells have zero average signal. Use of this method facilitates the selection of rare cells transfected with surface antigen genes. Culture conditions affect the level of autofluorescence and the balance between red and green autofluorescence. When applied with fluorescein-conjugated reagents, the technique is compatible with the use of propidium iodide for live/dead cell discrimination.