Attentional selection and attentional gradients: An alternative method for studying transient visual-spatial attention

In two experiments, I employed an alternative method for studying transient visual-spatial attention. Instead of using precuse, attention was manipulated by presenting most stimuli sequentially at predictable locations. In Experiment 1, most stimuli appeared in a regular clockwise or counterclockwise order, but some were separated by one or both visual meridians from the expected location. In Experiment 2, most stimuli were presented succesively along the horizontal meridian, and some stimuli were separated by one, two, or three positions from the expected location. Faster response times and larger posterior P1 and N1 components as well as enhanced negativities at midline electrodes were found for expected-location than for unexpected-location stimuli. These effects were partially modulated by the distance of unexpected stimuli from the current focus of attention, suggesting the existence of attentional gradients. Moreover, the data suggest that the direction of previous attentional shifts and the visual meridians play an important role for spatial attention.     

Shift of attention to the body location of distracters is mediated by perceptual load in sustained somatosensory attention

We investigated the impact of task difficulty on neuronal facilitation of to-be-attended somatosensory vibrotactile stimuli and transient tactile distracters during sustained attention. In Experiment 1, we employed an easy detection task and in Experiment 2 a challenging discrimination task. Sustained attention was manipulated by presenting vibrotactile stimuli simultaneously to the index fingers of both hands for a period of 3 s. These stimuli elicited the steady-state somatosensory evoked potential (SSSEP). Subjects attended to one body side and had to detect target-stimuli that were embedded in the ongoing vibratory streams. When subjects discriminated target-stimuli we found increased SSSEP amplitudes of the to-be-attended vibrotactile stream and greater N140 amplitudes of the somatosensory evoked potential (SEP). During stimulus detection no such facilitation of the SSSEP was found. Greater N140 amplitudes elicited by to-be-ignored distracters indicated that they pull attention to that body location under conditions of low load.     

The Effect of Predictability on Evoked Response Enhancement in Intramodal Selective Attention

We investigated the relationship between the attention enhancement of the visual average evoked response (AER) and the S's ability to predict the presentation of the attended stimulus. Twelve students were presented with sequences of two distinct visual stimuli while DC EEG and electro-oculogram (EOG) were simultaneously recorded. Stimuli were either regularly alternated (predictable) or randomly intermixed (nonpredictable). Verbal instructions directed S's attention and push button response to either one or both of the two stimuli. Interstimulus interval was held constant to permit computer averaging of the AER and the contingent negative variation. Selective attention enhanced the late positive component of the AER equally in the two conditions of predictability. Thus, it seems that the AER enhancement with intramodal selective attention does not depend on the S's ability to predict the presentation of the attended stimulus or to differentially arouse prior to its presentation. In the high predictability condition, the baseline EEG potential fluctuated with attention such that the AERs to the attended stimuli were negative relative to those to the ignored stimuli.     

Event-Related Potentials During Memory Search and Selective Attention to Letter Size and Conjunctions of Letter Size and Color

The analysis of event-related potentials was used in two experiments to investigate the structure of information processing in a task in which subjects selectively attended to letter size (Experiment 1) or a conjunction of letter size and color (Experiment 2) and searched for target letters within the attended stimulus category. The event-related potentials showed that selective attention to letter size resulted in the enhancement of a central N2b component (onset about 200 ms), which was assumed to reflect feature nonspecific orienting of attention. When attention was directed to conjunctions of letter size and color an earlier effect was found (onset about 150 ms) consisting of positivity at the anterior electrodes and negativity at OZ. This earlier effect was assumed to reflect feature-specific selective processing. Although the early effect showed a hierarchical pattern of results, in which the effect of attending to size was contingent on the relevance of the color attribute, the N2b showed a more independent pattern of results, in which the relevance of either the color or the size attribute resulted in an enhancement of this component, independent of the relevance of the other attribute. An increase in the duration of the memory search process resulted in a prolonged negativity with an onset of about 200 ms which was maximal at CZ. In both experiments the initial phase of this negativity was also found in the event-related potentials to the unattended stimulus categories, suggesting that the search process was initiated nonselectively and terminated after the selection cues were identified. Detection of attended target letters resulted in a parietal P3b component. In both experiments there was an earlier effect discriminating targets and nontargets in the range 200-300 ms.     

Orienting of attention and eye movements

According to the premotor theory of attention, the mechanisms responsible for spatial attention and the mechanisms involved in programming ocular saccades are basically the same. The aim of the present experiments was to test this claim. In experiment 1 subjects were presented with a visual display consisting of a fixation point and four boxes arranged horizontally and located above the fixation cross. Two of the boxes were in the left visual hemifield, two in the right. A fifth box was located on the vertical meridian below the fixation cross. Digit cues indicated in which of the upper boxes the imperative stimulus was most likely to appear. Subjects were instructed to direct attention to the cued box and to perform a saccadic eye movement to the lower box on presentation of the imperative stimulus. The trajectory of the saccades deviated contralateral to the hemifield in which the imperative stimulus was presented. This deviation was larger when the hemifield where the imperative stimulus was presented was the cued one. In experiment 2, the visual display consisted of five boxes forming a cross. The central box served as a fixation point. The cue was a small line, linked to the central box, pointing to different directions and indicating where the visual imperative stimulus would appear. In 50% of trials, the imperative stimulus was a visual stimulus presented either in one of the lateral boxes or in the central one. In the remaining 50% of trials, the imperative stimulus was a non-lateralised sound. Half the subjects were instructed to make a saccade to the upper box at the presentation of the visual imperative stimulus and to the lower box at the presentation of the acoustic stimulus. Half the subjects received the opposite instructions. The results confirmed that the saccades deviate contralateral to the hemifield of stimulus presentation in the case of visual imperative stimuli. Most importantly, they showed that the saccades deviate contralateral to the cued hemifield, also in the case of acoustic imperative stimuli. Experiment 3 was similar to experiment 2. It confirmed the results of that experiment and showed that slow ocular drifts, which are observed in the time interval between cue and imperative stimulus presentation, cannot explain the ocular deviations. Taken together, the experiments demonstrate that spatial attention allocation leads to an activation of oculomotor circuits, in spite of eye immobility.     

The effect of emotional and attentional load on attentional startle modulation

The interactive effects of emotion and attention on attentional startle modulation were investigated in two experiments. Participants performed a discrimination and counting task with two visual stimuli during which acoustic eyeblink startle-eliciting probes were presented at long lead intervals. In Experiment 1, this task was combined with aversive Pavlovian conditioning. In Group Attend CS+, the attended stimulus was followed by an aversive unconditional stimulus (US) and the ignored stimulus was presented alone whereas the ignored stimulus was paired with the US in Group Attend CS−. In Experiment 2, a non-aversive reaction time task US replaced the aversive US. Regardless of the conditioning manipulation and consistent with a modality non-specific account of attentional startle modulation, startle magnitude was larger during attended than ignored stimuli in both experiments. Blink latency shortening was differentially affected by the conditioning manipulations suggesting additive effects of conditioning and discrimination and counting task on blink startle.     

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.     

Brain Potentials During Selective Attention, Memory Search, and Mental Rotation

Event-related potentials were measured in a task that combined the classic selective attention paradigm with memory search and mental rotation paradigms. Subjects were required to attend to stimulus letters in one color and to ignore stimuli in a different color. Within the attended category subjects searched for target letters from a prememorized set (the memory set) and indicated whether they were presented normally or in mirror-image. Letters in all stimulus categories were presented randomly in either their upright position or rotated over 60 degrees, 120 degrees, or 180 degrees. The event-related potentials showed that the earliest effect of attending to color was a positivity at the anterior electrodes and a negativity at Oz (onset about 150 ms), followed by the enhancement of a central N2 component (N2b, onset about 220 ms). The early effect is thought to reflect selective processing of elementary stimulus features, the later N2b the covert orienting of attention. A later, prolonged central negativity elicited by attended stimuli covaried with the duration of the memory search process. Target detection resulted in a parietal P3b component, and also in an earlier negativity (in the range approximately 200-300 ms) to both attended and unattended targets, suggesting an early preattentive target classification. There were two effects of the rotation of stimuli. First there was an early occipital effect (about 200-300 ms), irrespective of attention and stimulus categories. It was argued that this effect reflected the preattentive identification of the orientation of the stimulus letters. A later (onset about 350-400 ms) parietal effect consisted of an increase in negativity as a function of the angle over which letters were rotated. This prolonged negativity had a later onset latency than the search-related negativity, and was restricted to the event-related potentials to target letters in the attended input channel. It was suggested that this component is the manifestation of a mental rotation process. It was argued that rotation-related negativity and memory search-related activity reflect operations in distinct working memory subsystems.     

Eye blinks: new indices for the detection of deception

Eyeblink variables were investigated while subjects performed a guilty knowledge test (Experiment 1) and a dual modality attention task (Experiment 2). In both experiments, the temporal distribution of blinks was analyzed using an automatic video based blink analysis system [Matsuo and Fukuda, Jpn. J. Physiol. Psychol. Psychophysiol., 14 (1996), 17]. In experiment 1, the blink rate pattern discriminated between relevant and irrelevant stimuli. In experiment 2, the blink rate peak after the auditory stimulus disappeared during visually attended tasks whereas the blink rate peak after the visual stimulus was significant during auditory attended tasks. It was suggested that eye blinks could be related to the selective attention and that eye blinks could provide an additional index for the detection of deception.     

Effects of eccentricity on the attention-related N2pc component of the event-related potential waveform

The N2pc ERP component has been widely used as a measure of lateralized visual attention. It is characterized by a negativity contralateral to the attended location or target, and it is thought to reflect contralaterally enhanced processing of attended information in intermediate to high levels of the ventral visual pathway. Given that the receptive fields in these areas often extend a few degrees into the ipsilateral hemifield, we might expect that near-midline stimuli would be processed by both the contralateral and ipsilateral hemispheres, resulting in a diminished N2pc. However, little is known about the effect of eccentricity on the N2pc component. To address this gap in knowledge, we recorded the EEG while participants performed a discrimination task with stimuli presented at one of five eccentricities (0°, 0.05°, 1°, 2°, 4° and 8° between the inner edge of the stimulus and the midline). We found that the N2pc amplitude remained relatively constant across eccentricities, including when the inner edge was at the midline, except that N2pc amplitude was reduced by more than 50% at the greatest eccentricity (8°). We also examined the contralateral positivity that often follows the N2pc. This positivity became progressively larger, and the transition from negative to positive occurred progressively later, as the eccentricity increased. These findings suggest that future experiments looking at the N2pc can use near-midline stimuli without compromising the N2pc amplitude, but should avoid large eccentricities. Implications about the neural generators of the N2pc are also discussed.     

Selective attention to spatial and non-spatial visual stimuli is affected differentially by age: effects on event-related brain potentials and performance data.

To assess selective attention processes in young and old adults, behavioral and event-related potential (ERP) measures were recorded. Streams of visual stimuli were presented from left or right locations (Experiment 1) or from a central location and comprising two different spatial frequencies (Experiment 2). In both experiments, results were compared in visual-only and visual+auditory stimulus context conditions. Participants were forced to respond fast in both experiments, while maintaining high accuracy. In Experiment 1, no behavioral effects of aging were found; however, an enlargement of the N1 component in the older age group suggested that older adults initial selection process was larger than that of young adults. A late frontal effect following the P300 elicited by attended non-targets was larger in the visual+auditory condition than in the visual-only condition in the old age group. This effect was interpreted as reflecting a memory update of the relevant target location. In Experiment 2, older adults made relatively more errors in the visual+auditory condition than in visual-only condition, more so than the young adults. Older adults' ERP data were also characterized by an enlargement of the occipital selection negativity, compared to the young age group. In contrast to experiment 1, no late frontal post-P3 effect could be found, suggesting that the memory trace of the relevant stimulus feature was updated less frequently, explaining the reduction in response accuracy in the visual+auditory stimulus context conditions.     

The attentional selection of spatial and non-spatial attributes in touch: ERP evidence for parallel and independent processes

To investigate the functional relationship between spatial and non-spatial attentional selectivity in somatosensory processing, event-related potentials (ERPs) were recorded to mechanical tactile stimuli, which were delivered to the right or left hand, and were low or high in frequency (Experiment 1), or soft or strong in intensity (Experiment 2). Participants' task was to attend to a specific combination of one stimulus location and one non-spatial attribute. Spatial attention was reflected in enhanced N140 components followed by a sustained attentional negativity. ERP effects of non-spatial attention (enhanced negativities to the attended frequency or intensity) were observed in the same latency range, suggesting that the attentional selection of relevant spatial and non-spatial attributes occurs in parallel. Most importantly, ERP correlates of attention directed to stimulus frequency and intensity were unaffected by the current focus of spatial attention. In contrast to vision, where the selective processing of non-spatial attributes is hierarchically dependent on selection by location, but similar to auditory attention, spatial and non-spatial attentional selectivity appear to operate independently in touch.     

Foveal attention modulates responses to peripheral stimuli

When attending to a visual object, peripheral stimuli must be monitored for appropriate redirection of attention and gaze. Earlier work has revealed precentral and posterior parietal activation when attention has been directed to peripheral vision. We wanted to find out whether similar cortical areas are active when stimuli are presented in nonattended regions of the visual field. The timing and distribution of neuromagnetic responses to a peripheral luminance stimulus were studied in human subjects with and without attention to fixation. Cortical current distribution was analyzed with a minimum L1-norm estimate. Attention enhanced responses 100-160 ms after the stimulus onset in the right precentral cortex, close to the known location of the right frontal eye field. In subjects whose right precentral region was not distinctly active before 160 ms, focused attention commonly enhanced right inferior parietal responses between 180 and 240 ms, whereas in the subjects with clear earlier precentral response no parietal enhancement was detected. In control studies both attended and nonattended stimuli in the peripheral visual field evoked the right precentral response, whereas during auditory attention the visual stimuli failed to evoke such response. These results show that during focused visual attention the right precentral cortex is sensitive to stimuli in all parts of the visual field. A rapid response suggests bypassing of elaborate analysis of stimulus features, possibly to encode target location for a saccade or redirection of attention. In addition, load for frontal and parietal nodi of the attentional network seem to vary between individuals.     

Beta3, a novel auxiliary subunit for the voltage gated sodium channel is upregulated in sensory neurones following streptozocin induced diabetic neuropathy in rat

Event-related brain potentials were recorded from healthy human subjects while they attended to one of two auditory stimulus channels (defined by location, left and right of a fixation point, and pitch) in order to detect rare target events. The distracting properties of periodic noise (vs. continuous noise, experiment 1) and backward speech (vs. forward speech, experiment 2) presented from a third speaker located behind the subjects were investigated. A typical attention effect with a larger negativity for attended tones was observed in both experiments. Backward speech led to a significantly reduced target detection rate for the first four stimuli after onset of the distractor accompanied by a reduced event-related brain potential (ERP)-attention effect and a reduced fronto-central N2b component for the target stimuli. This indicates that irrelevant information leads to an attention decrement of about 1 s duration.     

Attentional modulations of event-related brain potentials sensitive to faces

Event-related brain potentials (ERPs) were recorded in response to centrally and peripherally presented faces and chairs under conditions where one stimulus category was attended and the other unattended. It was studied whether selective attention affects ERP components sensitive to the presence of faces. When compared with chairs, faces elicited larger N1 amplitudes at lateral temporal electrodes and a midline positivity in the same latency range. The latter effect was only found for central faces. Attention to centrally presented faces was reflected in enhanced posterior N1 amplitudes. This effect may be related to an attentional modulation of processing within face-specific brain areas. It was not elicited by chairs or peripheral faces. Beyond 200msec post-stimulus, a category-unspecific attentional negativity was found at all recording sites for centrally and peripherally presented face and nonface stimuli.     

ATTENTIONAL MODULATIONS OF EVENT-RELATED BRAIN POTENTIALS SENSITIVE TO FACES

Event-related brain potentials (ERPs) were recorded in response to centrally and peripherally presented faces and chairs under conditions where one stimulus category was attended and the other unattended. It was studied whether selective attention affects ERP components sensitive to the presence of faces. When compared with chairs, faces elicited larger N1 amplitudes at lateral temporal electrodes and a midline positivity in the same latency range. The latter effect was only found for central faces. Attention to centrally presented faces was reflected in enhanced posterior N1 amplitudes. This effect may be related to an attentional modulation of processing within face-specific brain areas. It was not elicited by chairs or peripheral faces. Beyond 200msec post-stimulus, a category-unspecific attentional negativity was found at all recording sites for centrally and peripherally presented face and nonface stimuli.     

Perceptual load modifies processing of unattended stimuli both in the presence and absence of attended stimuli

This study explored effects of perceptual load on stimulus processing in the presence and absence of an attended stimulus. Participants were presented with a bilateral or unilateral display and asked to perform a discrimination task at either low or high perceptual load. Electrophysiological responses to stimuli were then compared at the P100 and N100. As in previous studies, perceptual load modified processing of attended and unattended stimuli seen at occipital scalp sites. Moreover, perceptual load modulated attention effects when the attended stimulus was presented at high perceptual load for unilateral displays. However, this was not true when the attended and unattended stimulus appeared simultaneously in bilateral displays. Instead, only a main effect of perceptual load was found. Reductions in processing contralateral to the unattended stimulus at the N100 provide support for Lavie's (1995) theory of selective attention.     

Intermodal attention affects the processing of the temporal alignment of audiovisual stimuli

The temporal asynchrony between inputs to different sensory modalities has been shown to be a critical factor influencing the interaction between such inputs. We used scalp-recorded event-related potentials (ERPs) to investigate the effects of attention on the processing of audiovisual multisensory stimuli as the temporal asynchrony between the auditory and visual inputs varied across the audiovisual integration window (i.e., up to 125 ms). Randomized streams of unisensory auditory stimuli, unisensory visual stimuli, and audiovisual stimuli (consisting of the temporally proximal presentation of the visual and auditory stimulus components) were presented centrally while participants attended to either the auditory or the visual modality to detect occasional target stimuli in that modality. ERPs elicited by each of the contributing sensory modalities were extracted by signal processing techniques from the combined ERP waveforms elicited by the multisensory stimuli. This was done for each of the five different 50-ms subranges of stimulus onset asynchrony (SOA: e.g., V precedes A by 125–75 ms, by 75–25 ms, etc.). The extracted ERPs for the visual inputs of the multisensory stimuli were compared among each other and with the ERPs to the unisensory visual control stimuli, separately when attention was directed to the visual or to the auditory modality. The results showed that the attention effects on the right-hemisphere visual P1 was largest when auditory and visual stimuli were temporally aligned. In contrast, the N1 attention effect was smallest at this latency, suggesting that attention may play a role in the processing of the relative temporal alignment of the constituent parts of multisensory stimuli. At longer latencies an occipital selection negativity for the attended versus unattended visual stimuli was also observed, but this effect did not vary as a function of SOA, suggesting that by that latency a stable representation of the auditory and visual stimulus components has been established.     

Stimulus-focused attention speeds up auditory processing

Stimulus-focused attention enhances the processing of auditory stimuli, which is indicated by enhanced neural activity. In situations where fast responses are required, attention may not only serve as a means to gain more information about the relevant stimulus, but it may provide a processing speed gain as well. In two experiments we investigated whether attentional focusing decreased the latency of the auditory N1 event related potential. In Experiment 1 slowly emerging, soft (20dB sensation level) sounds were presented in two conditions, in which participants performed a sound-detection task or watched a silent movie and ignored the sounds. N1 latency was shorter in the sound-detection task in comparison to the ignore condition. In Experiment 2 we investigated whether the attentional N1 latency-decrease was caused by a frequency-specific attentional preparation or not. To this end, tone sequences were presented with a single tone frequency or with four different frequencies. N1 latency was shorter in the sound-detection task in comparison to the ignore condition regardless the number of frequencies. These results suggest that stimulus-focused attention increases stimulus processing speed by generally increasing sensory gain.     

Attentional selection in the processing of hierarchical patterns: an ERP study

The current study aimed to investigate the effect of attentional selection of distinctive local elements on the processing of hierarchically organized patterns. Event-related brain potentials (ERPs) were recorded from subjects during identifications of global or local shapes of hierarchical patterns where either all local elements were identical (homogeneous stimulus) or a local element closest to fixation was distinguished by color from others (pop-out stimulus). One group of subjects was presented with the homogeneous stimuli and required to identify global or local shapes in separate blocks of trials. The other group was presented with the pop-out stimuli and asked to attend to the unique local item in the local task. A global precedence effect was observed in behavioral data. ERPs showed enlarged posterior P1 and N2 amplitudes in the local relative to global conditions. Top-down attention to the pop-out item resulted in increased frontal/central N2 amplitudes in the local condition but eliminated the temporal/occipital N2 enhancement in the local relative to global conditions. Top-down attention to the pop-out item also increased local-to-global interference in reaction times and frontal N2 latencies. The results suggest that a frontal mechanism is involved in directing top-down attention to a specific local item whereas a temporal/occipital mechanism is engaged in an attentional filtering process in the identification of local shapes in hierarchical analysis.