The effect of startle reflex habituation on cardiac defense: Interference between two protective reflexes

The present study investigated the relationship between blink startle and cardiac defense, two protective reflexes that are said to be elicited by the transient and the sustained components, respectively, of high intensity stimuli. Three groups of participants were presented with three intense long lasting noise stimuli (500ms) after habituation training with 12 brief (50ms) high intensity noise bursts (High group), low intensity noise bursts (Low group) or high intensity visual stimuli (Light group). The transition from habituation to defense stimuli resulted in increased blink startles in groups Low and Light, but not in group High. A cardiac defense reflex, characterised by a short and long delayed increase in heart rate, was observed in group Light, but not in groups Low and High. This pattern of results indicates that habituation to startle eliciting stimuli will impair defense reflexes elicited on subsequent test trials and suggests some interrelation between the two reflex systems.     

Habituation and sensitization of protective reflexes: Dissociation between cardiac defense and eye-blink startle

We examined the habituation and recovery of two protective reflexes, cardiac defense and eye-blink startle, simultaneously elicited by a white noise of 500 ms as a function of the time interval between stimulus presentations. Participants were 90 volunteers (54 women) randomly distributed into 6 inter-trial interval (ITI) conditions. They all received three presentations of the stimulus with a time interval of 30 min between the first and third noise. The timing of the second noise was manipulated in six steps, using a between-group design, in order to increase the ITI between Trials 1 and 2 and symmetrically decrease the ITI between Trials 2 and 3. Cardiac defense showed fast habituation at the shortest ITI (2.5 min), but reduced habituation and increased recovery at the longest ITI (27.5 min). In contrast, eye-blink startle showed sensitization irrespective of the ITI. This pattern of findings highlights dissociations between protective reflexes when simultaneously examined. The results are discussed in the context of the cascade model of defense reactions.     

Differentiation between protective reflexes: cardiac defense and startle

Rise time and duration are two parametric characteristics of the eliciting stimulus frequently used to differentiate among psychophysiological reflexes. The present research varied the duration (study 1) and rise time (study 2) of an intense acoustic stimulus to dissociate cardiac defense and cardiac startle using the eyeblink response as the external criterion of startle. In each study, 100 participants were presented with five white noise stimuli of 105 dB under one of five duration (50, 100, 250, 500, and 1000 ms) or rise time (0, 24, 48, 96, and 240 ms) conditions. Cardiac defense was affected by stimulus duration, present only in the 500- and 1000-ms conditions, but not by stimulus rise time, present in all rise time conditions. Rise time affected blink startle, but did not selectively alter the short latency accelerative component of the heart rate response, thus questioning whether it reflects startle.     

Cardiac defense: from attention to action.

The concept of defense relates to the idea that organisms react physiologically to the presence of danger or threat in order to protect themselves from potential injury or death. This article reviews the literature on cardiac defense, a specific defense reaction that has a long tradition in psychophysiological research. The review begins with a brief analysis of the two traditional approaches to understand this autonomic response: the cognitive -- linked to Pavlov, Sokolov, and Graham's work on sensory reflexes -- and the motivational -- linked to Cannon and Selye's work on the concepts of activation and stress. Then, the classic model of cardiac defense and its basic assumptions concerning differentiation from other cardiac reflexes -- namely orienting and startle -- are presented. A critical analysis of these assumptions follows centered on evidence from a systematic research of the cardiac response to intense acoustic stimulation. Finally, an integrative model of cardiac defense is presented which emphasizes the dynamic nature of this defense reaction - characterized by a complex pattern of heart rate changes with accelerative and decelerative components, with sympathethic and parasympathetic influences, and with both attentional and motivational significance - providing a new framework in which the two opposite traditional approaches can be reconciled.     

Orienting of visual attention in dyslexia: evidence for asymmetric hemispheric control of attention

The purpose of this study was to determine whether the transport of small hydrophilic molecules across the blood-brain barrier (BBB) during focal cerebral ischemia could be altered by a topical application of endothelin-1 (ET-1) in the ischemic cortex (IC). Forty minutes after middle cerebral artery (MCA) occlusion, patches of 10 nM ET-1 (low-endothelin group), 100 nM ET-1 (high-endothelin group), or normal saline (control group) were placed on the IC of rats for a 20-min period. One hour after MCA occlusion, transfer coefficient (K _i) of [¹⁴C-α-]aminoisobutyric acid (¹⁴C-AIB) or regional cerebral blood flow (rCBF) was determined. Vital signs were not significantly different among the experimental groups. In the control group (n=8), the K _i of the IC was significantly higher than that of the contralateral cortex (CC; 11.9±5.8 vs 5.0±1.9 μl/g per minute). In the low-endothelin group (n=8), the K _i of the IC was still significantly higher than that of the CC (9.4±5.2 vs 5.3±2.5 μl/g per minute). However, in the High-endothelin group (n=8), the K _i of the IC was not different from that of the CC (6.9±2.1 vs 5.6±2.3 μl/g per minute) and 42% lower than that of the control group. The rCBF was not affected by 100 nM of ET-1 [control (n=6): IC 53±18 ml/100 g per minute, CC 94±23 ml/100 g per minute; high-endothelin (n=6): IC 49±15 ml/100 g per minute, CC 98±24 ml/100 g per minute]. Our data suggest that the application of endothelin-1 in the IC could reduce the transfer coefficient of small hydrophilic molecules across the BBB during focal ischemia. Electronic Publication     

Selective attention and response inhibition alter phase-dependent cardiac slowing

This study examined the effects of visual selective attention and stimulus discriminability on phasic heart rate changes. Grating stimuli consisting of four vertical bars were presented left or right from fixation. Participants attended to one side of the screen and responded with a button press to attended target stimuli that were defined by shorter middle bars. Stimulus discriminability was manipulated by increasing the length of the middle bars of targets. To examine the time course of response inhibition, participants had to respond to auditory probe stimuli that were presented occasionally and unpredictably at varying intervals following the visual stimulus. Responses to targets and probes following attended nontargets were slower in the difficult condition. Heart rate slowed in anticipation of a target and accelerated back to baseline afterwards. Phase-dependent cardiac slowing was larger for attended nontargets compared to unattended nontargets and was more pronounced in the difficult condition. These findings were interpreted vis-à-vis inhibition accounts of phase-dependent cardiac slowing.     

ERP correlates of anticipatory attention: spatial and non-spatial specificity and relation to subsequent selective attention

Brain-based models of visual attention hypothesize that attention-related benefits afforded to imperative stimuli occur via enhancement of neural activity associated with relevant spatial and non-spatial features. When relevant information is available in advance of a stimulus, anticipatory deployment processes are likely to facilitate allocation of attention to stimulus properties prior to its arrival. The current study recorded EEG from humans during a centrally-cued covert attention task. Cues indicated relevance of left or right visual field locations for an upcoming motion or orientation discrimination. During a 1 s delay between cue and S2, multiple attention-related events occurred at frontal, parietal and occipital electrode sites. Differences in anticipatory activity associated with the non-spatial task properties were found late in the delay, while spatially-specific modulation of activity occurred during both early and late periods and continued during S2 processing. The magnitude of anticipatory activity preceding the S2 at frontal scalp sites (and not occipital) was predictive of the magnitude of subsequent selective attention effects on the S2 event-related potentials observed at occipital electrodes. Results support the existence of multiple anticipatory attention-related processes, some with differing specificity for spatial and non-spatial task properties, and the hypothesis that levels of activity in anterior areas are important for effective control of subsequent S2 selective attention.     

The spatial distribution of visual attention in developmental dyslexia

The present study investigated the spatial distribution of visual attention in dyslexic and normally reading children. The performances of the two groups were investigated using two different paradigms. In experiment 1 we analyzed the distribution of processing resources both inside and outside the focus of visual attention by simply recording reaction times to the detection of a white dot target projected at different eccentricities from the fovea. The distribution of attentional resources differed significantly between the two groups of children. The eccentricity of the stimulus was significant only for normally reading children - who showed a normal gradient - as it influenced their detection speed, whereas it had no effect on dyslexic children, who exhibited a diffused distribution of visual processing resources inside the visual field. In experiment 2 we studied the distributed (unfocused) mode of attention in a visual search task by measuring reaction times to a target stimulus inside a large configuration with a variable number of distractors. Results show that as compared to normal children dyslexics are better able to distribute their attentional resources diffusely. Our conclusion is that reading disability may be characterized by a diffused distribution of visual processing resources. These data might be interpreted in the framework of studies on magnocellular deficits in dyslexia, whereby the anomalous distribution of visual attention might explain how transient pathway functioning influences the reading process.     

ERP effects of intermodal attention and cross-modal links in spatial attention

Effects of intermodal attention and of cross-modal links in spatial attention on visual and auditory event-related potentials (ERPs) were investigated in two experiments where participants had to attend to one stimulus modality (audition or vision) to respond to infrequently presented targets whenever these were presented at a relevant location (indicated by a cue). The ERP effects of intermodal attention (measured by comparing the ERPs elicited by visual and auditory stimuli when the respective modality was relevant or irrelevant) were differently distributed in vision and audition, suggesting that intermodal attention operates by a selective modulation of modality-specific areas. Similar ERP effects of spatial attention (measured by comparing the ERPs to stimuli at cued and uncued locations) were elicited at midline electrodes in vision and audition. With one notable exception, these effects were also present when attention was directed within the other modality, suggesting the existence of cross-modal links between vision and audition in the control of transient spatial attention.     

Modulation of event-related potentials by word repetition: The role of visual selective attention

Event-related potentials (ERPs) were recorded while subjects viewed visually presented words, some of which occurred twice. Each trial consisted of two colored letter strings, the requirement being to attend to and make a word/non word discrimination for one of the strings. Attention was manipulated by color in Experiment 1, and color and a precue were used in Experiment 2. As in previous ERP studies of word repetition, a positive offset to repeated words developed when both first and second presentations were the focus of attention. In Experiment 2, ERPs showed evidence of positive-going repetition effects in all conditions in which at least one of the two presentations of the repeated word was attended. In the visual modality, the positive-going ERP repetition effect occurs only when at least one of the two presentations of a repeated item is the object of attention, which suggests that one or more of the processes reflected by the effect is capacity limited.     

Abnormal temporal dynamics of visual attention in Alzheimer's disease and in dementia with Lewy bodies

Although attentional control processes are disproportionately impaired in dementia with Lewy bodies (DLB) compared with dementia of the Alzheimer type (DAT), previous studies have not compared directly the temporal dynamics of visual attention in DLB and DAT. We examined the magnitude of the attentional blink (AB) effect in these patients, to determine the degree to which each patient group exhibited a deficit in selecting and processing visual stimuli presented in rapid succession. Eighteen DAT, 15 DLB patients, and 33 elderly controls were tested in a rapid serial visual presentation task. Participants were asked to report 1 (single-target condition) or 2 target letters (dual-target condition) embedded in a sequence of digit distracters. The temporal dynamics of visual attention was examined by varying the number of intervening distracters between the 2 targets in the dual-target condition and by estimating the attentional blink effect as the decline in the ability to report the second target correctly after successfully identifying the first. Patients with DLB performed significantly worse than patients with DAT and controls in both the single and dual-targets conditions. In contrast, DAT patients showed a selective impairment in the dual-target condition as compared with controls. As predicted, we found that both patients with DAT and DLB showed a more pronounced and protracted attentional blink than controls, indicating a reduced ability to re-engage attention on the second target. Furthermore, when DAT and DLB patients were able to report the second target, they frequently failed to identify the first, an effect that was absent in elderly controls and particularly large and long-lasting in DLB patients. This study suggests that both DLB and DAT patients show abnormal temporal dynamics of visual selective attention, presumably due to a greater intertarget competition for limited processing capacity. More generally, these findings reinforce the notion that deficits of attentional control processes are more severe in DLB patients as compared with DAT patients.     

The N2pc component and its links to attention shifts and spatially selective visual processing

The N2pc component has recently become a popular tool in attention research. To investigate whether this component exclusively reflects attentional target selection or also prior stages in attentional processing (covert orienting, target-unspecific spatial attention), a spatial cuing procedure was combined with a visual search task. In some blocks, informative cues indicated the side of upcoming singleton targets that were present on most trials among uniform distractors. In other blocks, cues were spatially uninformative, and no preparatory shifts of attention were possible. The N2pc in response to targets was unaffected by this manipulation, showing that this component is not associated with attention shifts. Following informative cues, an attenuated N2pc was elicited by uniform nontarget arrays, suggesting that the N2pc may also reflect spatially specific processing of stimulus features at task-relevant locations prior to target selection.     

Toward the influence of temporal attention on the selection of targets in a visual search task: An ERP study

We used ERPs to investigate whether temporal attention interacts with spatial attention and feature‐based attention to enhance visual processing. We presented a visual search display containing one singleton stimulus among a set of homogenous distractors. Participants were asked to respond only to target singletons of a particular color and shape that were presented in an attended spatial position. We manipulated temporal attention by presenting a warning signal before each search display and varying the foreperiod (FP) between the warning signal and the search display in a blocked manner. We observed distinctive ERP effects of both spatial and temporal attention. The amplitudes for the N2pc, SPCN, and P3 were enhanced by spatial attention indicating a processing benefit of relevant stimulus features at the attended side. Temporal attention accelerated stimulus processing; this was indexed by an earlier onset of the N2pc component and a reduction in reaction times to targets. Most importantly, temporal attention did not interact with spatial attention or stimulus features to influence visual processing. Taken together, the results suggest that temporal attention fosters visual perceptual processing in a visual search task independently from spatial attention and feature‐based attention; this provides support for the nonspecific enhancement hypothesis of temporal attention.     

The internal control of action and Parkinson's disease: a kinematic analysis of visually-guided and memory-guided prehension movements

This paper reports two experiments which examined the effects of Parkinson's disease (PD) upon the sensorimotor mechanisms used to control prehension movements. Transport and grasp kinematics for visually-guided and memory-guided prehension movements were examined in healthy control subjects and compared against those of patients with idiopathic PD. Two research questions were addressed: (1) Are patients with PD particularly susceptible to distraction by non-relevant objects? (2) Are patients with PD especially reliant on external feedback when executing goal-directed actions? The results indicated that the patient group were no more susceptible to distraction by non-relevant objects than the control group. In contrast, the patients with PD were shown to be significantly, impaired when executing memory-guided reaches. Furthermore, the deficits exhibited by the PD group on memory-guided reaches were confined solely to those markers associated with the transport component of the prehension movement. That is, while both controls and patients with PD widened their grip aperture on memory-guided trials, the magnitude of this adjustment was comparable across the two groups. The implications of these findings for theories of visuomotor processing in sufferers of PD and the control of prehension movements more generally are discussed.     

Acute effects of caffeine on selective attention and visual search processes

The influence of a single dose of caffeine was evaluated in focused and divided attention conditions of a visual selective search task in which subjects had to perform controlled search processes to locate a target item. Search processes were manipulated by varying display load. A dose of 3 mg/kg body weight caffeine or lactose, dissolved in a cup of decaffeinated coffee, was administered double blindly and deceptively to overnight abstinent coffee drinkers. Behavioral measures were supplemented by event-related potentials (ERPs). Subjects reacted faster in the caffeine condition. The P3b peak latency decreased after caffeine in the low display load condition and in the focused attention condition, indicating that the effects of caffeine are dependent on the number of relevant display items, not on the total number of display items presented. Search processes, as reflected in a negative ERP deflection, were not affected by caffeine.     

Location and features of instructive spatial cues do not influence the time course of covert shifts of visual spatial attention

The time course of shifting visual spatial attention to flickering stimuli in the left and right visual hemifield was investigated. The goal was to test whether an instructive peripheral salient cue located close to the newly to-be-attended location triggers faster shifts per se compared to a central cue. Besides behavioural data an objective electrophysiological measure, the steady-state visual evoked potential (SSVEP) was used to measure the time course of visual pathway facilitation in the human brain for centrally and peripherally cued shifts of spatial attention. Results revealed that both spatial cues resulted in identical time courses of shifts of covert spatial attention. This was true with respect to behavioural data and SSVEP amplitude. Results support the notion that a salient peripheral spatial cue does not automatically produce faster shifts of spatial attention to the to-be-attended location when this cue is informative and embedded in an ongoing stimulation.     

To gamble or not to gamble: at risk for craving and relapse--learned motivated attention in pathological gambling

In recent research similarities between pathological gambling and drug addiction have been identified, suggesting excessive gambling to constitute an addiction. So far, we have insufficient knowledge concerning the psychophysiological mechanisms underlying this kind of non-substance-related addiction. The objective of the study was to investigate emotional processing of gambling-relevant and -irrelevant stimuli in pathological gamblers and non-gambling controls using an EEG cue-reactivity paradigm. Whereas gambling-irrelevant stimuli were processed similarly in non-gambling controls (HC) and pathological gamblers (PG), PG showed significantly stronger gambling-relevant stimulus-induced psychophysiological cue-reactivity (larger gambling stimulus-induced late positive potential, LPP, higher arousal and more positively toned valence ratings as well as higher stimulus-induced craving for gambling cues compared to HC - but not the expectable increase of general craving over time and after stimulus presentation). Our findings suggest enhanced cue-reactivity in pathological gamblers indicative of learned motivated attention that may induce subjective craving and relapse.     

The middle range of the number line orients attention to the left side of visual space

Mental representation of numbers is believed to be spatial in nature, with small numbers occupying the left and large numbers the right side of a putative mental number line. Consistent with this, presentation of numbers from the low and high ends of the mental number line induces covert shifts of spatial attention to the left and right side of visual space, respectively. However, the effect of the presentation of the middle range (containing numbers below and above the midpoint) of the number line on visual perception has so far not been studied. Here we show in two experiments, using a line bisection task and a simple target detection task, that processing of middle-range numbers affects allocation of visuospatial attention in a similar way as processing of small numbers, with attention shifted to the left side of space. We suggest that this pattern of results arises due to “anchoring” heuristics that participants use in number processing.     

Increased blood flow in the basal ganglia when using cues to direct attention

We used positron emission tomography (PET) in ten subjects to study the brain regions involved in voluntary shifts of attention. For six scans, subjects performed a visual target detection task in which the location of the target was indicated in advance on some proportion of trials by the appearance of an arrow cue at fixation. The informative cues were successful in speeding reaction time to the target. Blood flow in the left putamen was correlated with the proportion of informative cues provided within a scan. We discuss this finding in terms of three possible interpretations: attentional shifts, response inhibition, and motor preparation related to the use of the right hand to respond. Blood flow in cortical regions commonly associated with attention was not related to cue ratio, a finding that may reflect automatization of the processes involved in interpreting and using the cues. Received: 23 February 1999 / Accepted: 13 June 1999     

The deployment of visual attention during temporal integration: an electrophysiological investigation

The deployment of attention during temporal integration was investigated with event-related potentials. Attentional selection of an integrated percept and an actual singleton were examined. Integration performance was related to modulations of the N2pc, N2, and P3 components. Singleton localization performance was reflected in N2pc and P3 only. Of note, the singleton N2pc developed and subsided earlier than the integration N2pc. The singleton P3 seemed to develop in a single deflection, while the integration P3 showed two more distinct deflections. Physical stimulus differences could not explain these results. The N2pc and N2 modulations showed that attending to an integrated percept is not slower per se, but does differ from attending to a singleton. Integrated percepts furthermore have special correlates in late stages of perception (i.e., the P3). These differences are linked to the unique demand to combine and represent successive stimuli.