Determinants of tonic and phasic reactions in transswitching

Forty-eight college students were assigned randomly to four groups in a 2 X 2 factorial arrangement of phasic conditional stimuli (same vs. different) and tonic conditional stimuli (same vs. different) to receive 2 days of classical conditioning with a transswitching procedure. Tonic stimuli were a 5-minute projected white triangle or circle; phasic stimuli were a 5-second red or green square superimposed over the tonic stimuli. There were six tonic stimulus segments each day, separated by 20-second periods of no stimulus, three containing six trials of the phasic stimulus paired with shock and three containing six trials of the phasic stimulus alone, in the counterbalanced order. Tonic responding at the onset of the tonic stimuli or during brief periods following its onset were recorded, along with phasic responses to the phasic stimuli. Responses included magnitude of skin conductance responses, frequency of unelicited skin conductance responses, and tonic heart rate. Both skin conductance measures of responding to the tonic stimuli differentiated significantly between positive and negative tonic segments during Day 2, but only in the group with two different tonic stimuli and one phasic stimulus ("standard" transswitching). This supported the hypothesis that tonic stimulus differentiation would be absent when two different phasic stimuli were present. The heart rate data did not support this hypothesis, showing tonic differentiation in both groups with two tonic stimuli. Phasic differentiation controlled by the different phasic stimuli was observed on Day 1; on Day 2, phasic differentiation was present only in the group with two tonic and one phasic stimuli and the group with one tonic and two phasic stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Contextual stimulus control of conditional vasomotor and electrodermal reactions to angry and friendly faces. Transswitching--yes! Preparedness--No!

An experiment with 42 human Ss used the transswitching procedure to examine tonic stimulus control of phasic and tonic conditioned vasomotor heart rate, and electrodermal reactions. The conditional stimulus (CSs) were photos of angry and friendly human faces, and the unconditional stimulus (US) was a human scream. In one tonic context (blue light), the CSs were paired with the US, in the other context (yellow light), the CSs were presented unpaired. Following acquisition, an extinction series was run with the US omitted during both tonic contexts. Phasic vasomotor and skin conductance reactions differed in the positive and negative tonic segments (stronger in positive). The skin conductance responses also differed during extinction, but the vasomotor responses did not. Tonic differences (following onset of the tonic stimuli) in unelicited skin conductance response frequency, finger pulse volume, and heart rate were also found, although these developed more slowly than the phasic differences. The finger pulse volume tonic difference was greater in extinction than the skin conductance response frequency. There was no effect of the angry-friendly facial expressions, either directly or in interaction with the transswitching effects. The results were interpreted to mean that the transswitching phenomenon is not limited to one another autonomic effector, but is more generalized across the ANS (sympathetic branch). The absence of influence of the facial expressions indicates the relative weakness of the "preparedness" hypothesis in comparison with more influential contextual factors.     

Contextual conditioning. A comparison of eastern and western views

Eastern and Western interpretations of contextual control of phasic conditional responses (transswitching) are contrasted. The Eastern (Asratyan, 1965) approach emphasizes the role of the tonic conditional stimulus and the (hypothetical) tonic response it evokes. The Western (Lachnit, 1986) approach emphasizes the role of compound conditional stimuli. Although Lachnit showed that transswitching-like results can be obtained without a tonic stimulus, attempts to simulate transswitching experiments using a computer model of the Rescorla-Wagner theory (Kimmel and Lachnit, 1988) have shown that predictions from the theory approximate empirical results in human classical conditioning only when the tonic stimulus is given far greater weight than the phasic stimulus. In other words, only when the Rescorla-Wagner theory is made more like Asratyan's theory, can the compound conditional stimulus approach account for real empirical transswitching data.     

Serial conditional discrimination and temporal bisection in rats selectively lesioned in the dentate gyrus

In positive serial conditional discrimination, animals respond during a target stimulus when it is preceded by a feature stimulus, but they do not respond when the same target stimulus is presented alone. Moreover, the feature and target stimuli are separated from each other by an empty interval. The present work aimed to investigate if two durations (4 or 16 s) of the same feature stimulus (light) could modulate the operant responses of rats to different levers (A and B) during a 5-s target stimulus (tone). In the present study, lever A was associated with the 4-s light, and lever B was associated with the 16-s light. A 5-s empty interval was included between the light and the tone. In the same training procedure, the rats were also presented with the 5-s tone without the preceding light stimuli. In these trials, the responses were not reinforced. We evaluated the hippocampal involvement of these behavioral processes by selectively lesioning the dentate gyrus with colchicine. Once trained, the rats were submitted to a test using probe trials without reinforcement. They were presented with intermediate durations of the feature stimulus (light) to obtain a temporal bisection curve recorded during the exposure to the target stimuli. The rats from both groups learned to respond with high rates during tones preceded by light and with low rates during tones presented alone, which indicated acquisition of the serial conditional discrimination. The rats were able to discriminate between the 4- and 16-s lights by correctly choosing lever A or B. In the test, the temporal bisection curves from both experimental groups showed a bisection point at the arithmetic mean between 4 and 16 s. Such processes were not impaired by the dentate gyrus lesion. Thus, our results showed that different durations of a feature stimulus could result in conditional properties. However, this processing did not appear to depend on the dentate gyrus alone.     

Effects of discrete visual feedback on the electrodermal control of a stressful situation

Two groups of human volunteers received three sessions of discriminated avoidance and punishment with the skin resistance response (SRR) as the operant. During each session one group (feedback) received three 6–8-min periods of Sidman avoidance of a 1.5-mA shock (R-S=40 sec, S-S=35 sec) mixed with three periods of punishment with a 20-sec time-out after each period. The avoidance and punishment periods were signaled by red and green lights, and a circle appeared superimposed on the discriminative stimuli for the duration of a criterion response. A second group (no feedback) received the same conditions as the feedback group except that no circle appeared. Instructions to the subject were not informative regarding experimental events. Subjects made significantly more SRR's during avoidance, a contingency in which responding prevented shock, than during punishment, a contingency in which responding produced shock. A reliable four-way interaction suggested that the feedback stimulus curtailed a tendency for avoidance response rate to diminish within and between experimental sessions. The data are considered as evidence for electrodermal (autonomic) control of two different stressful situations, and the potential value of the paradigm for establishing tonic autonomic arousal and suppression is considered.This research was supported by the Charles L. Mix Memorial Fund. The data were collected in part by M. D. McCrary.     

Startle responding and context conditioning. Naloxone pretreatment and stimulus intensity

The possibility that acoustic startle stimuli could support a conditional response (freezing) to contextual stimuli was investigated. Rats were exposed to three acoustic startle stimuli on the first day, and one on the second day. On day 1, 20 rats received naloxone pretreatment and another 20 received saline (placebo) pretreatment. Half of each group received a high-intensity acoustic stimulus, the other half a low-intensity acoustic stimulus. Both the higher stimulus intensity and the naloxone pretreatment led to greater freezing behavior during the 3-minute test period before the single startle stimulus on day 2. These findings support the notion that increased actual or perceived intensity of the acoustic startle stimulus increases conditioning to contextual stimuli as indexed by freezing behavior.     

Acquisition of visually guided conditional associative tasks in Göttingen minipigs

Fourteen Göttingen minipigs were trained on two different visually guided conditional associative tasks. In a spatial conditional task, a black stimulus signalled that a response to the left was correct, and a white stimulus signalled that a response to the right was correct. In a conditional go/no-go task, a blue stimulus signalled go, and a red stimulus signalled no-go. The pigs were trained until a behavioural criterion of 90% correct for each of two consecutive sessions. For the spatial conditional task, all pigs reached this criterion in 520 trials or less. For the conditional go/no-go task, all pigs, except three, reached this criterion in 1600 trials or less. Sows and boars learned equally fast. The tasks can be useful for the testing of cognitive function in pig models of human brain disorders.     

Pavlovian conditioning with proximal stimuli

This experiment was conducted with the objective of demonstrating that the effective stimuli in Pavlovian Conditioning are not environmental stimuli but internal physiological processes elicited by environmental input (proximal stimuli). In order to achieve the objective, afterimages in color vision were used: looking at a diffuse lightened circle after seeing a red circle yields an image of a green circle. A differential conditioning paradigm with two sequential compounds was run. In one group (G+B-: n1 = 10), a red circle followed by a green circle was paired with shock, whereas a red circle followed by a blue circle remained unpaired. A second group (G-B+: n2 = 10) received red-blue paired trials and unpaired red-green trials. Immediately after that training, subjects were tested with a new, never trained sequential compound: a red circle followed by a diffuse lightened circle. Furthermore, they were tested with the already trained compounds. Taking the environmental point of view, the never trained stimulus should elicit an orienting response lying in between the excitatory reaction to the paired stimulus and the inhibitory reaction to the unpaired stimulus. From the proximal point of view, the diffuse light should elicit an excitatory reaction in group G+B- and an inhibitory reaction in group G-B+. Electrodermal conditioned anticipatory and omission responses were measured. The results supported the proximal hypothesis. Hence, defining input in environmental terms may be the wrong way. Instead, in conceptualizing the stimulus in conditioning, the following should be considered: the processing organism itself is creating the effective stimuli.     

The role of terminal-link stimuli in concurrent-chain schedules: revisited using a behavioral-history procedure

A behavioral-history procedure was used to study the function of terminal-link stimuli as conditioned reinforcers in multiple concurrent-chain schedules of reinforcement. First, three pigeons were exposed to multiple concurrent-chain schedules in which the two multiple-schedule components were correlated with a blue and a white stimulus, respectively. In each component the initial links were equal independent variable-interval (VI) 15 s schedules. A fixed-interval (FI) 10 s schedule operated on the red key in one terminal link while extinction operated on the green key in the alternative terminal link. When large preferences for the red stimulus had been established, two tests were conducted. In the terminal-link test, under new initial-link stimuli--purple and brown--an FI 10 s schedule operated for both the red and green terminal-link stimuli. In the subsequent initial-link test, the blue and white initial-link stimuli were reintroduced, and, as in the terminal-link test, FI 10s operated for both the red and the green terminal-link stimuli. In the terminal-link test, the three pigeons showed no preference for the terminal links with the red stimulus, but showed clear and consistent preferences for the red stimulus when blue and white stimuli were reintroduced as initial-link stimuli in the initial-link test. This suggests that there are multiple sources of control over initial-link response allocation in concurrent-chains, including control by both terminal- and initial-link stimuli.     

Relation between warning stimuli and contingent negative variation in man

Seven right handed male students were submitted to standard and target paired auditory stimuli to determine the relationship between contingent negative variation (CNV) and the slow negative waves following non paired stimuli. The warning stimuli informed subjects whether or not the impending unconditional stimulus implied a motor response. Subjects were instructed to execute the motor task at less than one second after unconditional stimulus. They were informed that the standard warning stimulus would be followed by an additional stimulus which confirmed its detection. Recordings of standard warning stimulus condition showed a subsequent increase in CNV amplitude. This significant increase appeared to be related to an enhancement in the subject's expectation towards the additional stimulus. The lowered CNV voltage in target condition seemed to be linked to the instructions, which involved a motor preparation after the imperative stimuli occurrence. It is suggested that the CNV may represent not only a general anticipatory but also an orienting process related to the signal value of the warning stimulus.     

Amiloride is an ineffective conditioned stimulus in taste aversion learning in C57BL/6J and DBA/2J mice

The epithelial sodium channel (ENaC) blocker amiloride has been shown to increase the behaviorally measured NaCl detection threshold in mice. In this study, a conditioned taste aversion (CTA) paradigm was used to examine whether 100 microM amiloride has a perceptible taste that could contribute to this observed decrease in behavioral responsiveness. Eighty-four C57BL/6J (B6) and 64 DBA/2J (D2) mice were divided into eight groups (n=8-12 per group), in which half received an injection of 0.15 M LiCl (2 mEq/kg) and the other half an equivalent saline injection, in three conditioning trials. The four conditioned stimuli were 100 microM amiloride hydrochloride, water, 0.1 and 0.3 M NaCl. Neither strain demonstrated acquisition of a CTA to amiloride in a brief-access (BA) taste test (5 s trials in the gustometer). Although 0.3 M NaCl is inherently aversive, its pairing with LiCl led to significantly further decreases in licking during the BA test on salt trials in both strains. The D2 strain clearly avoided 0.1 M NaCl, whereas avoidance of this stimulus was more equivocal in B6 mice. The inefficacy of amiloride to serve as a conditioned stimulus in taste aversion learning involving three LiCl pairings suggests that the effects of this ENaC blocker on taste-related behavioral responses to NaCl are likely due to its pharmacological interference with sodium taste transduction.     

Laboratory conditioning to still or flowing water does not affect the responses to a food stimulus by red swamp crayfish (Procambarus clarkii) in flowing water habitats

We tested the role of hydrodynamics in the use of chemical signals by the red swamp crayfish (Procambarus clarkii). We conditioned the crayfish in either a still water or flowing water habitat for 2 weeks. We then observed the crayfish in control (no stimulus) and experimental (food stimulus) trials in one of two flowing water habitats-laminar or turbulent. Habitat use was significantly different between control and experimental observations, but there was no effect of conditioning habitat or experimental habitat on the responses to the food stimulus. This study adds to a growing body of literature consistent with the idea that gross responses to chemical stimuli in crayfish are not affected by the hydrodynamic context in which they are encountered.     

Effects of Different Spectra from LED on the Growth,Development and Reproduction of <i>Arabidopsis thaliana</i>

Light is the major source of energy for plants and as such has a profound effect on plant growth and development. Red and blue lights have been considered to best drive photosynthetic metabolism and are beneficial for plant growth and development, and green light was seen as a signal to slow down or stop. In this study, Arabidopsis thaliana (Arabidopsis) was used to investigate the effects of red, blue and green lights on the growth and development of plants from seed germination to seeding. Results demonstrated that red light showed a promotion effect but blue light a prohibition one in most stages except for the flowering time in which the effect of each light was just reversed. When mixed with red or blue light, green light generally at least partially cancelled out the effects caused by each of them. Results also showed that the same number of photons the plant received could cause different effects and choosing the right combination of different color of lights is essential in both promoting the growth and development of plants and reducing the energy consumption of lighting in plant factory.     

Cortical activation changes during repeated laser stimulation: a magnetoencephalographic study

Repeated warm laser stimuli produce a progressive increase of the sensation of warmth and heat and eventually that of a burning pain. The pain resulting from repetitive warm stimuli is mediated by summated C fibre responses. To shed more light on the cortical changes associated with pain during repeated subnoxious warm stimulation, we analysed magnetoencephalographic (MEG) evoked fields in eleven subjects during application of repetitive warm laser stimuli to the dorsum of the right hand. One set of stimuli encompassed 10 laser pulses occurring at 2.5 s intervals. Parameters of laser stimulation were optimised to elicit a pleasant warm sensation upon a single stimulus with a rise of skin temperature after repeated stimulation not exceeding the threshold of C mechano-heat fibres. Subjects reported a progressive increase of the intensity of heat and burning pain during repeated laser stimulation in spite of only mild (4.8°C) increase of skin temperature from the first stimulus to the tenth stimulus. The mean reaction time, evaluated in six subjects, was 1.33 s, confirming involvement of C fibres. The neuromagnetic fields were modelled by five equivalent source dipoles located in the occipital cortex, cerebellum, posterior cingulate cortex, and left and right operculo-insular cortex. The only component showing statistically significant changes during repetitive laser stimulation was the late component of the contralateral operculo-insular source peaking at 1.05 s after stimulus onset. The amplitude increases of the late component of the contralateral operculo-insular source dipole correlated with the subjects' numerical ratings of warmth and pain. Results point to a pivotal role of the contralateral operculo-insular region in processing of C-fibre mediated pain during repeated subnoxious laser stimulation.     

Effect of chronic intermittent exposure to AM radiofrequency field on responses to various types of noxious stimuli in growing rats

There are several reports of altered pain sensation after exposure (from a few minutes to hours in single or repeated doses for 2-3 weeks) to electromagnetic fields (EMF) in adults. The commonly utilized noxious stimulus is radiant heat. The nociceptive responses are known to be influenced by characteristics of stimulus, organism, and environment. We studied the pattern of nociceptive responses to various noxious stimuli in growing rats exposed to radiofrequency field (73.5 MHz amplitude modulated, 16 Hz power density 1.33 mw/cm(2), SAR = 0.4 w/kg) for 45 d (2 h/d). Threshold current for stimulation of nociceptive afferents to mediate motor response of tail (TF), vocalization during stimulus (VD), and vocalization after discharge (VA); the withdrawal latency of tail (TFL) and hind paw (HPL) to thermal noxious stimulus and tonic pain responses were recorded in every rat. The TFL was not affected, HPL was decreased (p < 0.01), and the thresholds of TF and VD were not affected, while, that of VA was significantly decreased. The tonic pain rating was decreased (p < 0.01). A decrease in the threshold of VA (p < 0.01) is indicative of an increase in the emotional component of the response to the phasic pain, whereas a decrease in the pain rating indicates analgesia in response to the tonic pain. The results of our study suggest that chronic (45 d), intermittent (2 h/d) amplitude modulated RF field exposure to the peripubertal rat increases the emotional component of phasic pain over a basal eaualgesic state, while late response to tonic pain is decreased. The data suggest that amplitude modulated RF field differentially affects the mechanisms involved in the processing of various noxious stimuli.     

Pavlovian conditional stimuli cannot always be defined solely in physical terms

Twenty-four university students received differential Pavlovian conditioning with two colored stimuli separately accompanied by shock, and two other colored stimuli separately presented without shock. The reinforced and nonreinforced pairs of stimuli both contained complementary elements. After differentiation between the reinforced and nonreinforced elements was established, the complementary pairs were each additively mixed, (i.e., presented at the same time and in the same locus), producing two identical white compounds (established by pilot study). The subjects' skin-conductance responses to the two compounds showed that their different conditioning histories did not result in different responses. Rather, a simple declining function was obtained, resembling habituation or extinction. It was concluded that the definition of the conditional stimulus as a physical event is inappropriate in studies in which physically different stimuli may result in identical internal processes (or phenomenologic experiences)--for example, in additive color mixture.     

The effects of cross-modal manipulations of attention on the detection of vibrotactile stimuli in humans

Although it is well known that attention to a visual or auditory stimulus can enhance its perception, less is known concerning the effects of attention on the perception of natural tactile stimuli. The present study was conducted to examine the magnitude of the effect of cross-modal manipulations of attention in human subjects on the detection of weak, low-frequency vibrotactile stimuli delivered to the glabrous skin of the finger pad of the right index finger via an Optacon. Three suprathreshold vibrotactile arrays (40 Hz), varying in the number of activated pegs and hence the area of skin stimulated, were used. Subjects were trained to detect the occurrence of vibrotactile or visual stimuli and to respond by pressing a foot pedal as quickly as possible thereafter. Two instructional lights were used to cue the subjects as to which stimulus modality they should attend, in three experimental conditions. In the first cue condition, the forthcoming stimulus modality was indicated by the illumination of its associated light. In the second cue condition, both instructional lights were illuminated, and the subjects were asked to divide their attention equally between the two modalities. In the third cue condition, the stimulus modality was falsely indicated by the illumination of the cue not associated with the stimulus to be presented. Reaction times (RTs) were calculated for each trial. For each modality, tactile and visual, the RTs varied significantly with the cue condition, with the mean RT changing in a graded manner across the experimental conditions (being shortest for the correctly cued condition, intermediate for the neutrally cued condition, and longest for the incorrectly cued condition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stimulus change dis-habituates operant responding supported by water reinforcers

The present experiment examined whether habituation contributes to within-session decreases in operant responding for water reinforcers. The experiment asked if this responding can be dishabituated, a fundamental property of habituated behavior. During baseline, rats’ lever pressing was reinforced by water on a variable interval 15-s schedule. During experimental conditions, rats responded on the same schedule and a new stimulus was introduced for 5 min at 15, 30 or 45 min into the 60-min session. The new stimulus was extinction, continuous reinforcement or flashing lights in different conditions. Rate of responding primarily decreased within the session during baseline. Introducing a new stimulus sometimes suppressed (extinction, continuous reinforcement) and sometimes increased (flashing lights) responding while it was in effect. The new stimulus increased responding after it ended and before it was presented in the session. The results are incompatible with the idea that non-habituation satiety factors (e.g., cellular hydration and blood volume) contributed to within-session changes in responding. These satiety factors should increase with increases in consumption, decrease with decreases in consumption and remain constant with constant consumption of water. Nevertheless, all stimulus changes increased operant responding for water. These results support the idea that habituation contributes to within-session decreases in responding for water reinforcers.     

Intradimensional and extradimensional shifts in conditional discrimination

Two groups of pigeons learned a two key conditional discrimination. Color was the conditional stimulus and form the choice stimulus for subjects in one group. Form was the conditional stimulus and color the choice stimulus in the other group. Half the subjects in each group then underwent an intradimensional shift: The conditional stimulus dimension and choice stimulus dimension were unchanged but the correct and incorrect stimulus compounds were reversed. The remaining subjects underwent an extra-dimensional shift in which the conditional stimulus dimension and choice stimulus dimension were reversed. Subjects which experienced an intradimensional shift learned the new conditional discrimination more quickly. It was concluded that subjects followed rules to solve conditional discriminations but also learned the functions of each stimulus dimension.     

Background gamma activity in the rabbit electroencephalogram as an index of the level of sustained (tonic) attention in the active oddball paradigm in rabbits

Tonic brain activity substantially affects the character of subjects' responsiveness to sensory stimuli. The dynamics of background gamma-band activity in rabbit electroencephalogram was investigated in the active oddball paradigm modified for animal studies. It was shown that increase in the power and coherence of gamma activity reflects the target stimulus expectancy. Correct responses to stimuli occur at a particular level of background gamma activity, which is likely to correspond to the optimal level of sustained (tonic) attention. Decrease in the level of background gamma activity leads to omissions of responses to target stimuli, while it's excessive level results in erroneous responses to nontarget stimuli (false alarms). The observed dynamics of tonic gamma activity can be interpreted as the result of variations in the level of tonic cholinergic activation of the brain cortex.