To test the classical conditioning and expectancy theories of placebo effects. Two experiments in... more To test the classical conditioning and expectancy theories of placebo effects. Two experiments investigated whether administration of caffeine-associated stimuli elicited conditioned arousal, and whether information that a drink contained or did not contain caffeine modulated arousal. Experiment 1 (n=21) used a 2 Caffeine (0 and 2 mg/kg) x 2 Solution (Coffee, Juice) x 2 Information (Told caffeine, Told not-caffeine) within-subjects design. Experiment 2 (n=48) used a 2 Solution (Coffee, Orange juice) x 3 Information (Told caffeine, Told not-caffeine, No information) between-subjects design. Indexes of arousal were skin conductance responses and levels, startle eyeblink reflexes, cardiovascular measures, and the Bond and Lader 1974 mood scale. Caffeine-associated stimuli increased alertness, contentedness and skin conductance levels, and information that the drink contained caffeine decreased calmness in Experiment 1. However, unexpected information about the caffeine content of the drink, and the order of the conditions, could have masked some effects of the experimental manipulations. Experiment 2 followed up this hypothesis. The results showed a conditioned increase in startle eyeblink reflexes, and that caffeine-associated stimuli together with information that the drink contained caffeine increased contentedness. Caffeine-associated stimuli increased arousal, and information about the content of the drink modulated arousal in the direction indicated by the information. Thus, both the classical conditioning and expectancy theories of placebo effects received support, and placebo effects were strongest when both conditioned responses and expectancy-based responses acted in the same direction.
Rationale: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits... more Rationale: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits the startle reflex. This is termed prepulse inhibition (PPI) and is postulated to index automatic and controlled attentional processing of the prepulse. Objective: Two experiments investigated the effect of 0, 2, and 4 mg/kg oral caffeine on PPI of the acoustic startle eyeblink reflex across stimulus onset asynchronies (SOAs) ranging from 30 to 420 ms. In experiment 1, acoustic prepulses were used and automatic attention was investigated, whereas in experiment 2, acoustic and tactile prepulses were used and automatic and controlled attention was investigated. Controlled attention was investigated by instructing the subjects to attend to one stimulus (attended stimulus) and not to another stimulus (non-attended stimulus). Methods: Caffeine was administrated to human subjects in within-subjects designs (n=24 and n=18). Startle reflexes to 100 dB noise were recorded by electromyography. A mood scale and readings of blood pressure indexed arousal. Results: Caffeine increased the indexes of arousal. There were, however, no significant main effects of caffeine on startle, nor did caffeine significantly interact with any other variable. Attended acoustic prepulses increased PPI at the 120 ms and longer SOAs. Caffeine 4 mg/kg abolished this difference between attended and non-attended stimuli. Attended tactile prepulses facilitated startle at short SOAs, and caffeine reduced facilitation of startle by tactile prepulses. Conclusions: Caffeine did not facilitate automatic attention. Caffeine 4 mg/kg abolished the effect of controlled attention on PPI. Facilitation of startle by attend-ed acoustic prepulses is best explained by facilitation of motoneurons in the facial nucleus.
Assessment of visual acuity was combined with observations of behavioral state indicating CNS act... more Assessment of visual acuity was combined with observations of behavioral state indicating CNS activation in 24 individuals with mental retardation. Visual acuity was assessed by presentations of Teller Acuity Cards on two occasions. Behavioral state was classified along a scale with four categories during visual acuity testing. Results showed good test-retest reliability for the Teller Acuity Cards. Six participants had different behavioral state scores on the two test occasions, but displayed similar visual acuity on both tests. No participant rated as "drowsy" displayed responses on the acuity test. Results indicate that forced-choice preferential-looking technique can be used to test visual acuity in this population unless the participant is drowsy.
Neuropsychiatric Disease and Treatment, Jun 1, 2008
A group of persons with dissociative identity disorder (DID) was compared with a group of persons... more A group of persons with dissociative identity disorder (DID) was compared with a group of persons with other dissociative disorders, and a group of nondiagnosed controls with regard to prepulse inhibition (PPI) of the acoustic startle refl ex. The fi ndings suggest maladaptive attentional processes at a controlled level, but not at a preattentive automatic level, in persons with DID. The prepulse occupied more controlled attentional resources in the DID group compared with the other two groups. Preattentive automatic processing, on the other hand, was normal in the DID group. Moreover, startle refl exes did not habituate in the DID group. In conclusion, increased PPI and delayed habituation is consistent with increased vigilance in individuals with DID. The present fi ndings of reduced habituation of startle refl exes and increased PPI in persons with DID suggest the operation of a voluntary process that directs attention away from unpleasant or threatening stimuli. Aberrant voluntary attentional processes may thus be a defi ning characteristic in DID.
Rationale: To test the theory that expectations control placebo responses. Objective: Subjects (n... more Rationale: To test the theory that expectations control placebo responses. Objective: Subjects (n=20) were asked how much they expected their arousal to increase after one or two cups of coffee, and were subsequently exposed to one or two cups of decaffeinated coffee, or to caffeine equivalent to one or two cups of coffee (200 and 400 mg). The expectancy theory of placebo responses predicts a positive correlation between expectations and actual placebo responses. Methods: Dependent variables were acoustic startle eyeblink and skin conductance responses, blood pressure and heart rate, and measures of subjective arousal. Results: Caffeine increased startle eyeblink and skin conductance responses, as well as blood pressure and subjective arousal. Decaffeinated coffee increased startle eyeblink and skin conductance responses, but had no effect on subjective arousal, although the participants clearly expected increased subjective arousal after both one and two cups of coffee. However, there were significant correlations between the alertness expected after coffee, and the actual alertness recorded after decaffeinated coffee. Conclusions: The main finding in this study was that relatively strong expectations about the effects of coffee did not generate placebo responses after administration of decaffeinated coffee. Expectations were dose dependent, whereas the placebo response was not. However, expected alertness after coffee predicted recorded alertness after coffee. In sum, the expectancy theory of placebo effects received only limited support.
Objective: Information that a painkiller has been administrated induces an expectancy of reduced ... more Objective: Information that a painkiller has been administrated induces an expectancy of reduced pain, and the expectancy has been shown to reduce pain. This is termed placebo analgesia. We hypothesized that an expectancy of reduced pain reduces stress. Methods: The present study (N=84) investigated this hypothesis. To further study the effects of stress and emotions on pain, we provided information about the pain stimulus to half the subjects. Pain was induced by the submaximum tourniquet technique.
ABSTRACT When a weak stimulus, or prepulse, is presented immediately prior to a startle reflex-el... more ABSTRACT When a weak stimulus, or prepulse, is presented immediately prior to a startle reflex-eliciting stimulus, the startle reflex is inhibited. This is called prepulse inhibition (PPI). Directing attention to a prepulse increases PPI. In two experiments (N = 43 and N = 29), attention was directed to the prepulse by having the participants judge the duration of the prepulse. Prepulse inhibition was assessed at stimulus onset asynchronies (SOAs) assumed to index automatic and controlled processing. The prepulse was a 60dB tone, and startle was elicited by 95dB white noise. We predicted that attention directed to the prepulse should increase PPI, and that PPI should increase on trials with correct judgments of prepulse duration compared to trials with incorrect judgments. The results from both experiments showed that attention directed toward the prepulse increased PPI at SOAs assumed to index both automatic and controlled processing. This indicates that controlled attention exerted an influence on automatic processes. There was no evidence that PPI was increased on trials with correct judgment of prepulse duration. It is concluded that attention to the prepulse increased PPI, but PPI did not differentiate between automatic and controlled processing under the present experimental conditions.
ABSTRACT In two experiments, we assessed the effects of directed attention on the elicitation and... more ABSTRACT In two experiments, we assessed the effects of directed attention on the elicitation and modification of the startle reflex. An acoustic startle stimulus was preceded on some trials by a tone at stimulus onset asynchronies (SOAs) of 120 or 240 msec (Experiment 1, N = 26) and 1,200 or 2,400 msec (Experiment 2, N = 24). On some trials, following the offset of the startle stimulus, either a tone or a tactile stimulus was presented to the hand (vibration in Experiment 1, airpuff in Experiment 2). On each of four blocks of trials, the subject was given one of the following tasks: Ignore all stimuli, or, when a particular tone prestimulus was presented (high frequency for some subjects, low frequency for others), judge the duration of (1) a tone following the startle stimulus, (2) a tactile stimulus following the startle stimulus, or (3) the startle stimulus itself. The subjects were instructed to ignore all the stimuli when the other tone prestimulus was presented. In the startle-probe-alone conditions, attending to the tactile stimulus increased acoustic startle reactivity (larger startle in Experiment 1, more probable and faster startle in Experiment 2) compared with startle in the ignore condition. Attending to the probe itself did not affect startle amplitude. Responding was similar when subjects attended to either the tone or the probe, suggesting that attention effects were modality specific, but not stimulus specific. Prestimuli at 120- and 240-msec SOAs inhibited startle amplitude in all cases, and this inhibition was more pronounced when attention was directed to any stimulus than in the ignore condition, showing nonspecific attentional effects at short SOAs. At longer SOAs, startle reflexes were inhibited more in the presence of nonsignal prestimuli than signal prestimuli. The increased startle reactivity, which occurred in both experiments when the subjects were required to shift attention from the auditory to the tactile modality, may have been due to greater task demands and, therefore, greater arousal in these conditions.
ABSTRACT The present studies evaluated the impact of an acoustic pulse on the human blink reflex ... more ABSTRACT The present studies evaluated the impact of an acoustic pulse on the human blink reflex elicited by an airpuff stimulus, when the acoustic stimulus was presented before, simultaneous with, or after the blink reflex-eliciting airpuff. The airpuff was presented at stimulus onset asynchronies (SOAs) relative to onset of a 70 dB noise of from -80 to 80 ms. In Experiment 1 (N = 13), reflex amplitude was facilitated at a 20 ms SOA, but only when a short response scoring window of 30 ms was used. In Experiment 2 (N = 12), subjects wore sound-attenuating headphones, in order to decrease the brief noise caused by the airpuff from 95 to 55 dB. In this situation, blink amplitude was Facilitated at SOAs of -20, 0, and 20 ms, but only in the 30 ms scoring window. in a third experiment (N = 20), the intensity of the noise accompanying the airpuff was manipulated directly. The results showed significantly increased blink reflexes when stronger (95 dB) as compared to weaker (55 dB) noise accompanied the airpuff. These findings replicate earlier findings of reflex facilitation when noise is presented at about the same time as the reflex-eliciting stimulus, and point to the importance of response parameters and the response scoring window when investigating reflex facilitation. The findings have implications For research that uses airpuffs as reflex-eliciting stimuli.
. Similar effects of attention directed to acoustic and tactile stimuli on prepulse inhibition of... more . Similar effects of attention directed to acoustic and tactile stimuli on prepulse inhibition of acoustic startle. Scandinavian Journal of Psychology , 44 , 363 -372. Prepulse inhibition (PPI) is assumed to index automatic and controlled processing. In three experiments ( n = 32, 22, and 30) participants were asked to judge the duration of a prepulse in comparison with a stimulus presented 4000 ms before the prepulse. A distracter was presented simultaneously with the prepulse to increase the cognitive demands of the task. PPI was assessed at stimulus onset asynchronies (SOAs) of 30-150 ms, and 420 ms. The prepulse was either a tone (60 dB) or a tactile stimulus (21 kPa), and startle was elicited by 95 dB white noise. Directing attention to the prepulse increased PPI at SOAs of 60 ms and longer in all experiments, but the sensory modality to which attention was directed played only a minor role. We conclude that directing attention to both acoustic and tactile prepulses increased PPI.
Several methods of quantifying prepulse inhibition (PPI) of eyeblink responding were compared in ... more Several methods of quantifying prepulse inhibition (PPI) of eyeblink responding were compared in adult volunteers. Blink-eliciting stimuli were noise bursts at 85 or 100 dB, and prepulses were also noise bursts, at 55 or 70 dB and lead intervals of 60 or 120 ms. PPI was evaluated by comparing reactivity on prepulse and control trials within participants using the following methods: (1) difference between reactivity on prepulse and control trials; (2) reactivity on prepulse trials divided by that on control trials (proportion of control); (3) difference between reactivity on prepulse and control trials, divided by that on control trials (proportion of the difference from control); (4) range correction (maximum minus minimum reactivity, divided by the range of reactivity), across all control and prepulse trials; (5) z scores across all prepulse and control trials. Prepulses inhibited eyeblink response magnitude in all cases. Proportion of difference was the method least affected by differences in control reactivity, and is the preferred method to use when quantifying PPI, both from a practical and a neurophysiological perspective. assessing prepulse effects on startle blink responding appeared in Psychophysiology. Of these, 10 (34%) used the raw difference method, 11 (38%) used the proportion of difference method, 7 (24%) used standardized scores, and 1 (3%) used range corrected scores. None used the proportion of control method.
Rationale: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits... more Rationale: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits the startle reflex. This is termed prepulse inhibition (PPI) and is postulated to index automatic and controlled attentional processing of the prepulse. Objective: Two experiments investigated the effect of 0, 2, and 4 mg/kg oral caffeine on PPI of the acoustic startle eyeblink reflex across stimulus onset asynchronies (SOAs) ranging from 30 to 420 ms. In experiment 1, acoustic prepulses were used and automatic attention was investigated, whereas in experiment 2, acoustic and tactile prepulses were used and automatic and controlled attention was investigated. Controlled attention was investigated by instructing the subjects to attend to one stimulus (attended stimulus) and not to another stimulus (non-attended stimulus). Methods: Caffeine was administrated to human subjects in within-subjects designs (n=24 and n=18). Startle reflexes to 100 dB noise were recorded by electromyography. A mood scale and readings of blood pressure indexed arousal. Results: Caffeine increased the indexes of arousal. There were, however, no significant main effects of caffeine on startle, nor did caffeine significantly interact with any other variable. Attended acoustic prepulses increased PPI at the 120 ms and longer SOAs. Caffeine 4 mg/kg abolished this difference between attended and non-attended stimuli. Attended tactile prepulses facilitated startle at short SOAs, and caffeine reduced facilitation of startle by tactile prepulses. Conclusions: Caffeine did not facilitate automatic attention. Caffeine 4 mg/kg abolished the effect of controlled attention on PPI. Facilitation of startle by attend-ed acoustic prepulses is best explained by facilitation of motoneurons in the facial nucleus.
To test the classical conditioning and expectancy theories of placebo effects. Two experiments in... more To test the classical conditioning and expectancy theories of placebo effects. Two experiments investigated whether administration of caffeine-associated stimuli elicited conditioned arousal, and whether information that a drink contained or did not contain caffeine modulated arousal. Experiment 1 (n=21) used a 2 Caffeine (0 and 2 mg/kg) x 2 Solution (Coffee, Juice) x 2 Information (Told caffeine, Told not-caffeine) within-subjects design. Experiment 2 (n=48) used a 2 Solution (Coffee, Orange juice) x 3 Information (Told caffeine, Told not-caffeine, No information) between-subjects design. Indexes of arousal were skin conductance responses and levels, startle eyeblink reflexes, cardiovascular measures, and the Bond and Lader 1974 mood scale. Caffeine-associated stimuli increased alertness, contentedness and skin conductance levels, and information that the drink contained caffeine decreased calmness in Experiment 1. However, unexpected information about the caffeine content of the drink, and the order of the conditions, could have masked some effects of the experimental manipulations. Experiment 2 followed up this hypothesis. The results showed a conditioned increase in startle eyeblink reflexes, and that caffeine-associated stimuli together with information that the drink contained caffeine increased contentedness. Caffeine-associated stimuli increased arousal, and information about the content of the drink modulated arousal in the direction indicated by the information. Thus, both the classical conditioning and expectancy theories of placebo effects received support, and placebo effects were strongest when both conditioned responses and expectancy-based responses acted in the same direction.
To test the classical conditioning and expectancy theories of placebo effects. Two experiments in... more To test the classical conditioning and expectancy theories of placebo effects. Two experiments investigated whether administration of caffeine-associated stimuli elicited conditioned arousal, and whether information that a drink contained or did not contain caffeine modulated arousal. Experiment 1 (n=21) used a 2 Caffeine (0 and 2 mg/kg) x 2 Solution (Coffee, Juice) x 2 Information (Told caffeine, Told not-caffeine) within-subjects design. Experiment 2 (n=48) used a 2 Solution (Coffee, Orange juice) x 3 Information (Told caffeine, Told not-caffeine, No information) between-subjects design. Indexes of arousal were skin conductance responses and levels, startle eyeblink reflexes, cardiovascular measures, and the Bond and Lader 1974 mood scale. Caffeine-associated stimuli increased alertness, contentedness and skin conductance levels, and information that the drink contained caffeine decreased calmness in Experiment 1. However, unexpected information about the caffeine content of the drink, and the order of the conditions, could have masked some effects of the experimental manipulations. Experiment 2 followed up this hypothesis. The results showed a conditioned increase in startle eyeblink reflexes, and that caffeine-associated stimuli together with information that the drink contained caffeine increased contentedness. Caffeine-associated stimuli increased arousal, and information about the content of the drink modulated arousal in the direction indicated by the information. Thus, both the classical conditioning and expectancy theories of placebo effects received support, and placebo effects were strongest when both conditioned responses and expectancy-based responses acted in the same direction.
Rationale: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits... more Rationale: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits the startle reflex. This is termed prepulse inhibition (PPI) and is postulated to index automatic and controlled attentional processing of the prepulse. Objective: Two experiments investigated the effect of 0, 2, and 4 mg/kg oral caffeine on PPI of the acoustic startle eyeblink reflex across stimulus onset asynchronies (SOAs) ranging from 30 to 420 ms. In experiment 1, acoustic prepulses were used and automatic attention was investigated, whereas in experiment 2, acoustic and tactile prepulses were used and automatic and controlled attention was investigated. Controlled attention was investigated by instructing the subjects to attend to one stimulus (attended stimulus) and not to another stimulus (non-attended stimulus). Methods: Caffeine was administrated to human subjects in within-subjects designs (n=24 and n=18). Startle reflexes to 100 dB noise were recorded by electromyography. A mood scale and readings of blood pressure indexed arousal. Results: Caffeine increased the indexes of arousal. There were, however, no significant main effects of caffeine on startle, nor did caffeine significantly interact with any other variable. Attended acoustic prepulses increased PPI at the 120 ms and longer SOAs. Caffeine 4 mg/kg abolished this difference between attended and non-attended stimuli. Attended tactile prepulses facilitated startle at short SOAs, and caffeine reduced facilitation of startle by tactile prepulses. Conclusions: Caffeine did not facilitate automatic attention. Caffeine 4 mg/kg abolished the effect of controlled attention on PPI. Facilitation of startle by attend-ed acoustic prepulses is best explained by facilitation of motoneurons in the facial nucleus.
Assessment of visual acuity was combined with observations of behavioral state indicating CNS act... more Assessment of visual acuity was combined with observations of behavioral state indicating CNS activation in 24 individuals with mental retardation. Visual acuity was assessed by presentations of Teller Acuity Cards on two occasions. Behavioral state was classified along a scale with four categories during visual acuity testing. Results showed good test-retest reliability for the Teller Acuity Cards. Six participants had different behavioral state scores on the two test occasions, but displayed similar visual acuity on both tests. No participant rated as "drowsy" displayed responses on the acuity test. Results indicate that forced-choice preferential-looking technique can be used to test visual acuity in this population unless the participant is drowsy.
Neuropsychiatric Disease and Treatment, Jun 1, 2008
A group of persons with dissociative identity disorder (DID) was compared with a group of persons... more A group of persons with dissociative identity disorder (DID) was compared with a group of persons with other dissociative disorders, and a group of nondiagnosed controls with regard to prepulse inhibition (PPI) of the acoustic startle refl ex. The fi ndings suggest maladaptive attentional processes at a controlled level, but not at a preattentive automatic level, in persons with DID. The prepulse occupied more controlled attentional resources in the DID group compared with the other two groups. Preattentive automatic processing, on the other hand, was normal in the DID group. Moreover, startle refl exes did not habituate in the DID group. In conclusion, increased PPI and delayed habituation is consistent with increased vigilance in individuals with DID. The present fi ndings of reduced habituation of startle refl exes and increased PPI in persons with DID suggest the operation of a voluntary process that directs attention away from unpleasant or threatening stimuli. Aberrant voluntary attentional processes may thus be a defi ning characteristic in DID.
Rationale: To test the theory that expectations control placebo responses. Objective: Subjects (n... more Rationale: To test the theory that expectations control placebo responses. Objective: Subjects (n=20) were asked how much they expected their arousal to increase after one or two cups of coffee, and were subsequently exposed to one or two cups of decaffeinated coffee, or to caffeine equivalent to one or two cups of coffee (200 and 400 mg). The expectancy theory of placebo responses predicts a positive correlation between expectations and actual placebo responses. Methods: Dependent variables were acoustic startle eyeblink and skin conductance responses, blood pressure and heart rate, and measures of subjective arousal. Results: Caffeine increased startle eyeblink and skin conductance responses, as well as blood pressure and subjective arousal. Decaffeinated coffee increased startle eyeblink and skin conductance responses, but had no effect on subjective arousal, although the participants clearly expected increased subjective arousal after both one and two cups of coffee. However, there were significant correlations between the alertness expected after coffee, and the actual alertness recorded after decaffeinated coffee. Conclusions: The main finding in this study was that relatively strong expectations about the effects of coffee did not generate placebo responses after administration of decaffeinated coffee. Expectations were dose dependent, whereas the placebo response was not. However, expected alertness after coffee predicted recorded alertness after coffee. In sum, the expectancy theory of placebo effects received only limited support.
Objective: Information that a painkiller has been administrated induces an expectancy of reduced ... more Objective: Information that a painkiller has been administrated induces an expectancy of reduced pain, and the expectancy has been shown to reduce pain. This is termed placebo analgesia. We hypothesized that an expectancy of reduced pain reduces stress. Methods: The present study (N=84) investigated this hypothesis. To further study the effects of stress and emotions on pain, we provided information about the pain stimulus to half the subjects. Pain was induced by the submaximum tourniquet technique.
ABSTRACT When a weak stimulus, or prepulse, is presented immediately prior to a startle reflex-el... more ABSTRACT When a weak stimulus, or prepulse, is presented immediately prior to a startle reflex-eliciting stimulus, the startle reflex is inhibited. This is called prepulse inhibition (PPI). Directing attention to a prepulse increases PPI. In two experiments (N = 43 and N = 29), attention was directed to the prepulse by having the participants judge the duration of the prepulse. Prepulse inhibition was assessed at stimulus onset asynchronies (SOAs) assumed to index automatic and controlled processing. The prepulse was a 60dB tone, and startle was elicited by 95dB white noise. We predicted that attention directed to the prepulse should increase PPI, and that PPI should increase on trials with correct judgments of prepulse duration compared to trials with incorrect judgments. The results from both experiments showed that attention directed toward the prepulse increased PPI at SOAs assumed to index both automatic and controlled processing. This indicates that controlled attention exerted an influence on automatic processes. There was no evidence that PPI was increased on trials with correct judgment of prepulse duration. It is concluded that attention to the prepulse increased PPI, but PPI did not differentiate between automatic and controlled processing under the present experimental conditions.
ABSTRACT In two experiments, we assessed the effects of directed attention on the elicitation and... more ABSTRACT In two experiments, we assessed the effects of directed attention on the elicitation and modification of the startle reflex. An acoustic startle stimulus was preceded on some trials by a tone at stimulus onset asynchronies (SOAs) of 120 or 240 msec (Experiment 1, N = 26) and 1,200 or 2,400 msec (Experiment 2, N = 24). On some trials, following the offset of the startle stimulus, either a tone or a tactile stimulus was presented to the hand (vibration in Experiment 1, airpuff in Experiment 2). On each of four blocks of trials, the subject was given one of the following tasks: Ignore all stimuli, or, when a particular tone prestimulus was presented (high frequency for some subjects, low frequency for others), judge the duration of (1) a tone following the startle stimulus, (2) a tactile stimulus following the startle stimulus, or (3) the startle stimulus itself. The subjects were instructed to ignore all the stimuli when the other tone prestimulus was presented. In the startle-probe-alone conditions, attending to the tactile stimulus increased acoustic startle reactivity (larger startle in Experiment 1, more probable and faster startle in Experiment 2) compared with startle in the ignore condition. Attending to the probe itself did not affect startle amplitude. Responding was similar when subjects attended to either the tone or the probe, suggesting that attention effects were modality specific, but not stimulus specific. Prestimuli at 120- and 240-msec SOAs inhibited startle amplitude in all cases, and this inhibition was more pronounced when attention was directed to any stimulus than in the ignore condition, showing nonspecific attentional effects at short SOAs. At longer SOAs, startle reflexes were inhibited more in the presence of nonsignal prestimuli than signal prestimuli. The increased startle reactivity, which occurred in both experiments when the subjects were required to shift attention from the auditory to the tactile modality, may have been due to greater task demands and, therefore, greater arousal in these conditions.
ABSTRACT The present studies evaluated the impact of an acoustic pulse on the human blink reflex ... more ABSTRACT The present studies evaluated the impact of an acoustic pulse on the human blink reflex elicited by an airpuff stimulus, when the acoustic stimulus was presented before, simultaneous with, or after the blink reflex-eliciting airpuff. The airpuff was presented at stimulus onset asynchronies (SOAs) relative to onset of a 70 dB noise of from -80 to 80 ms. In Experiment 1 (N = 13), reflex amplitude was facilitated at a 20 ms SOA, but only when a short response scoring window of 30 ms was used. In Experiment 2 (N = 12), subjects wore sound-attenuating headphones, in order to decrease the brief noise caused by the airpuff from 95 to 55 dB. In this situation, blink amplitude was Facilitated at SOAs of -20, 0, and 20 ms, but only in the 30 ms scoring window. in a third experiment (N = 20), the intensity of the noise accompanying the airpuff was manipulated directly. The results showed significantly increased blink reflexes when stronger (95 dB) as compared to weaker (55 dB) noise accompanied the airpuff. These findings replicate earlier findings of reflex facilitation when noise is presented at about the same time as the reflex-eliciting stimulus, and point to the importance of response parameters and the response scoring window when investigating reflex facilitation. The findings have implications For research that uses airpuffs as reflex-eliciting stimuli.
. Similar effects of attention directed to acoustic and tactile stimuli on prepulse inhibition of... more . Similar effects of attention directed to acoustic and tactile stimuli on prepulse inhibition of acoustic startle. Scandinavian Journal of Psychology , 44 , 363 -372. Prepulse inhibition (PPI) is assumed to index automatic and controlled processing. In three experiments ( n = 32, 22, and 30) participants were asked to judge the duration of a prepulse in comparison with a stimulus presented 4000 ms before the prepulse. A distracter was presented simultaneously with the prepulse to increase the cognitive demands of the task. PPI was assessed at stimulus onset asynchronies (SOAs) of 30-150 ms, and 420 ms. The prepulse was either a tone (60 dB) or a tactile stimulus (21 kPa), and startle was elicited by 95 dB white noise. Directing attention to the prepulse increased PPI at SOAs of 60 ms and longer in all experiments, but the sensory modality to which attention was directed played only a minor role. We conclude that directing attention to both acoustic and tactile prepulses increased PPI.
Several methods of quantifying prepulse inhibition (PPI) of eyeblink responding were compared in ... more Several methods of quantifying prepulse inhibition (PPI) of eyeblink responding were compared in adult volunteers. Blink-eliciting stimuli were noise bursts at 85 or 100 dB, and prepulses were also noise bursts, at 55 or 70 dB and lead intervals of 60 or 120 ms. PPI was evaluated by comparing reactivity on prepulse and control trials within participants using the following methods: (1) difference between reactivity on prepulse and control trials; (2) reactivity on prepulse trials divided by that on control trials (proportion of control); (3) difference between reactivity on prepulse and control trials, divided by that on control trials (proportion of the difference from control); (4) range correction (maximum minus minimum reactivity, divided by the range of reactivity), across all control and prepulse trials; (5) z scores across all prepulse and control trials. Prepulses inhibited eyeblink response magnitude in all cases. Proportion of difference was the method least affected by differences in control reactivity, and is the preferred method to use when quantifying PPI, both from a practical and a neurophysiological perspective. assessing prepulse effects on startle blink responding appeared in Psychophysiology. Of these, 10 (34%) used the raw difference method, 11 (38%) used the proportion of difference method, 7 (24%) used standardized scores, and 1 (3%) used range corrected scores. None used the proportion of control method.
Rationale: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits... more Rationale: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits the startle reflex. This is termed prepulse inhibition (PPI) and is postulated to index automatic and controlled attentional processing of the prepulse. Objective: Two experiments investigated the effect of 0, 2, and 4 mg/kg oral caffeine on PPI of the acoustic startle eyeblink reflex across stimulus onset asynchronies (SOAs) ranging from 30 to 420 ms. In experiment 1, acoustic prepulses were used and automatic attention was investigated, whereas in experiment 2, acoustic and tactile prepulses were used and automatic and controlled attention was investigated. Controlled attention was investigated by instructing the subjects to attend to one stimulus (attended stimulus) and not to another stimulus (non-attended stimulus). Methods: Caffeine was administrated to human subjects in within-subjects designs (n=24 and n=18). Startle reflexes to 100 dB noise were recorded by electromyography. A mood scale and readings of blood pressure indexed arousal. Results: Caffeine increased the indexes of arousal. There were, however, no significant main effects of caffeine on startle, nor did caffeine significantly interact with any other variable. Attended acoustic prepulses increased PPI at the 120 ms and longer SOAs. Caffeine 4 mg/kg abolished this difference between attended and non-attended stimuli. Attended tactile prepulses facilitated startle at short SOAs, and caffeine reduced facilitation of startle by tactile prepulses. Conclusions: Caffeine did not facilitate automatic attention. Caffeine 4 mg/kg abolished the effect of controlled attention on PPI. Facilitation of startle by attend-ed acoustic prepulses is best explained by facilitation of motoneurons in the facial nucleus.
To test the classical conditioning and expectancy theories of placebo effects. Two experiments in... more To test the classical conditioning and expectancy theories of placebo effects. Two experiments investigated whether administration of caffeine-associated stimuli elicited conditioned arousal, and whether information that a drink contained or did not contain caffeine modulated arousal. Experiment 1 (n=21) used a 2 Caffeine (0 and 2 mg/kg) x 2 Solution (Coffee, Juice) x 2 Information (Told caffeine, Told not-caffeine) within-subjects design. Experiment 2 (n=48) used a 2 Solution (Coffee, Orange juice) x 3 Information (Told caffeine, Told not-caffeine, No information) between-subjects design. Indexes of arousal were skin conductance responses and levels, startle eyeblink reflexes, cardiovascular measures, and the Bond and Lader 1974 mood scale. Caffeine-associated stimuli increased alertness, contentedness and skin conductance levels, and information that the drink contained caffeine decreased calmness in Experiment 1. However, unexpected information about the caffeine content of the drink, and the order of the conditions, could have masked some effects of the experimental manipulations. Experiment 2 followed up this hypothesis. The results showed a conditioned increase in startle eyeblink reflexes, and that caffeine-associated stimuli together with information that the drink contained caffeine increased contentedness. Caffeine-associated stimuli increased arousal, and information about the content of the drink modulated arousal in the direction indicated by the information. Thus, both the classical conditioning and expectancy theories of placebo effects received support, and placebo effects were strongest when both conditioned responses and expectancy-based responses acted in the same direction.
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Papers by Magne Flaten