Attention and the perception of temporal order.

The effect of directing attention to a particular location in space has been widely examined in the study of human information processing. Current models assume that attention modulates the speed of information flow such that attended signals are transmitted more rapidly through the perceptual system than unattended signals. This assumption that attention modulates the speed of information flow was examined in the present research by having observers judge the temporal order of two visual stimuli while directing their attention towards one of the stimuli or away from both stimuli. In one experiment, attended stimuli were perceived with a shorter latency than unattended stimuli, supporting the assumption that attention influences the speed of information transmission in the visual system. The results of another experiment indicate that attention alters the temporal profile of the visual responses, such that visual responses at the attended location are more sharply tuned than responses at the unattended location. It is concluded that attention has two effects on visual responses: It affects the transmission speed of information in the visual system and it alters the temporal profile of the responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of inter- and intramodal selective attention to non-spatial visual stimuli: an event-related potential analysis

Event-related potentials (ERPs) were recorded to trains of rapidly presented auditory and visual stimuli. ERPs in conditions in which subjects attended to different features of visual stimuli were compared with ERPs to the same type of stimuli when subjects attended to different features of auditory stimuli. This design permitted us to study effects of variations in both intramodal and intermodal visual attention on the timing and topography of ERP components in the same experiment. There were no indications that exogenous N110, P140 and N180 components to line gratings of high and low spatial frequencies were modulated by either intra- or intermodal forms of attention. Furthermore, intramodal and intermodal attention effects on ERPs showed similar topographical distributions. These combined findings suggest that the same neural generators in extrastriate occipital areas are involved in both forms of attention. Visual ERPs elicited in the condition in which subjects were engaged in auditory selective attention showed a large positive displacement at the occipital scalp sites relative to ERPs to attended and unattended stimuli in the visual condition. The early onset of this positivity might be associated with a highly confident and early rejection of the irrelevant visual stimuli, when these stimuli are presented among auditory stimuli. In addition, the later onset of selection potentials in the intramodal condition suggests that a more precise stimulus selection is needed when features of visual stimuli are rejected among other features of the same stimulus pattern, than when visual stimuli are rejected among stimuli of another modality.     

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

Event-related potential (ERP) effects of transient and sustained non-spatial visual attention were investigated in an experiment where subjects were instructed to attend to the color or form of visual stimuli in order to detect infrequently presented targets with the relevant feature. The to-be-attended feature was either varied in a trial-by-trial fashion (transient attention) or was kept constant for an entire experimental block (sustained attention). Both transient and sustained attention resulted in a larger negativity for attended as compared to unattended stimuli between 200 and 300 ms post-stimulus. This effect was more pronounced for sustained attention than for transient attention and larger for attention to color than for attention directed to stimulus form. In the sustained, but not in the transient attention condition, color attention resulted in larger positivities for attended stimuli between 150 and 200 ms and in the P3 time range. These effects are interpreted as evidence for the existence of non-spatial attentional selection processes that are more effective under sustained than under transient attention conditions and are different from processes of visual-spatial attention. Moreover, the results indicate a special status for sustained attention to stimulus color.     

Inattention magnifies perceived length: The attentional receptive field hypothesis.

Five experiments demonstrated that a briefly presented vertical line is judged as longer when it is unattended relative to when it is attended. This effect was obtained in estimating the length of 1 of 5 possible lines (Experiment 1) and in matching the length of a test line to a criterion line (Experiments 3 and 4). The directional effect of attention was eliminated when participants estimated the length difference between 2 simultaneously presented lines (Experiment 2). An additional matching experiment (Experiment 5) demonstrated similar lengthening effects for unattended lines and for unattended distances separated by vertically displaced dots. It is proposed that the metric for unattended stimuli is composed of large attentional receptive fields and that the final output is mediated by rounding up processes, so that the unattended line is systematically perceived as longer than the attended one. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

External noise distinguishes attention mechanisms

We developed and tested a powerful method for identifying and characterizing the effect of attention on performance in visual tasks as due to signal enhancement, distractor exclusion, or internal noise suppression. Based on a noisy Perceptual Template Model (PTM) of a human observer, the method adds increasing amounts of external noise (white gaussian random noise) to the visual stimulus and observes the effect on performance of a perceptual task for attended and unattended stimuli. The three mechanisms of attention yield three "signature" patterns of performance. The general framework for characterizing the mechanisms of attention is used here to investigate the attentional mechanisms in a concurrent location-cued orientation discrimination task. Test stimuli--Gabor patches tilted slightly to the right or left--always appeared on both the left and the right of fixation, and varied independently. Observers were cued on each trial to attend to the left, the right, or evenly to both stimuli, and decide the direction of tilt of both test stimuli. For eight levels of added external noise and three attention conditions (attended, unattended, and equal), subjects' contrast threshold levels were determined. At low levels of external noise, attention affected threshold contrast: threshold contrasts for non-attended stimuli were systematically higher than for equal attention stimuli, which were, in turn, higher than for attended stimuli. Specifically, when the rms contrast of the external noise is below 10%, there is a consistent 17% elevation of contrast threshold from attended to unattended condition across all three subjects. For higher levels of external noise, attention conditions did not affect threshold contrast values at all. These strong results are characteristic of a signal enhancement, or equivalently, an internal additive noise reduction mechanism of attention.     

The rotatory machines in the history of psychiatry

In this study, we recorded the event-related potentials (ERPs) elicited by stimuli appearing at attended and unattended locations. The voltage amplitudes and latencies of the P1, N1, P2, N2 and P3 visual components showed statistically significant differences in the attended condition with respect to the unattended one. The power spectral density of the EEG following stimulus onset was calculated. The difference between the spectral densities of the attended and unattended conditions was computed. Statistically significant differences were found in the decrease of alpha (9-11 Hz) and the increase of beta (15-17 Hz) frequencies during the attention condition with respect to the unattended condition. These results suggest that the arrival of a visual stimulus during the attended condition generates a complex reorganization of neuronal activity in both time and frequency domains.     

Effects of stimulus modality and task condition on blink startle modification and on electrodermal responses

Participants in Experiments 1 and 2 performed a discrimination and counting task to assess the effect of lead stimulus modality on attentional modification of the acoustic startle reflex. Modality of the discrimination stimuli was changed across subjects. Electrodermal responses were larger during task-relevant stimuli than during task-irrelevant stimuli in all conditions. Larger blink magnitude facilitation was found during auditory and visual task-relevant stimuli, but not for tactile stimuli. Experiment 3 used acoustic, visual, and tactile conditioned stimuli (CSs) in differential conditioning with an aversive unconditioned stimulus (US). Startle magnitude facilitation and electrodermal responses were larger during a CS that preceded the US than during a CS that was presented alone regardless of lead stimulus modality. Although not unequivocal, the present data pose problems for attentional accounts of blink modification that emphasize the importance of lead stimulus modality.     

Visual offsets facilitate saccadic latency: Does predisengagement of visuospatial attention mediate this gap effect?

Saccadic reaction time (RT) is reduced when a fixation stimulus is extinguished 200 msec before a target appears. An attentional predisengagement theory (APT) may explain this gap effect: When covert attention is engaged (e.g., on fixation), the saccadic system is inhibited and RT is delayed; when the attended stimulus is extinguished, attention is disengaged, the inhibition is removed, and RT is facilitated. In 3 experiments covert attention was endogenously or exogenously cued to an object on the vertical meridian. Onset of a saccadic target on the horizontal meridian could be preceded by the offset of an attended or unattended object. Contrary to APT, RTs were identical after attended and unattended offsets. Results suggest that the gap effect has 2 components, and covert visual attention plays no role. One component is motor system preparation; the other is a fixation offset effect specific to the oculomotor system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Processing of auditory stimuli during auditory and visual attention as revealed by event-related potentials

Auditory event-related brain potentials (ERPs) were recorded during auditory and visual selective attention tasks. Auditory stimuli consisted of frequent standard tones (1000 Hz) and infrequent deviant tones (1050 Hz and 1300 Hz) delivered randomly to the left and right ears. Visual stimuli were vertical line gratings randomly presented on a video monitor at mean intervals of 6 s. During auditory attention, the subject attended to the stimuli in a designated ear and responded to the 1300-Hz deviants occurring among the attended tones. During visual attention, the subject responded to the occasional visual stimuli. ERPs for tones delivered to the attended ear were negatively displaced relative to ERPs elicited by tones delivered to the unattended ear and to ERPs elicited by auditory stimuli during visual attention. This attention effect consisted of negative difference waves with early and late components. Mismatch negativities (MMNs) were elicited by 1300-Hz and 1050-Hz deviants irrespective of whether they occurred among attended or unattended tones. MMN amplitudes were unaffected by attention, supporting the proposal that the MMN is generated by an automatic cerebral discrimination process.     

How do we select perceptions and actions? Human brain imaging studies

The selective nature of human perception and action implies a modulatory interaction between sensorimotor processes and attentional processes. This paper explores the use of functional imaging in humans to explore the mechanisms of perceptual selection and the fate of irrelevant stimuli that are not selected. Experiments with positron emission tomography show that two qualitatively different patterns of modulation of cerebral blood flow can be observed in experiments where non-spatial visual attention and auditory attention are manipulated. These patterns of modulation of cerebral blood flow modulation can be described as gain control and bias signal mechanisms. In visual and auditory cortex, the dominant change in cerebral blood flow associated with attention to either modality is related to a bias signal. The relation of these patterns of modulation to attentional effects that have been observed in single neurons is discussed. The existence of mechanisms for selective perception raises the more general question of whether irrelevant ignored stimuli are nevertheless perceived. Lavie's theory of attention proposes that the degree to which ignored stimuli are processed varies depending on the perceptual load of the current task. Evidence from behavioural and functional magnetic resonance imaging studies of ignored visual motion processing is presented in support of this proposal.     

Orthography, familiarity, and meaningfulness reconsidered: Attentional strategies may affect the lexical sensitivity of visual code formation.

Three same–different matching experiments used strings of letters as stimuli to explore the influence of orthography, familiarity, and lexical meaningfulness on visual code formation for words. In Experiment 1, larger effects of lexical meaningfulness occurred under conditions of visual stimulus degradation than when stimuli were bright and easy to resolve. Experiments 2 and 3 included diagnostics of two strategies (selective or divided attention) and showed that either could occur, but that only one produced the interaction. In the selective or visual, pattern of results which was observed in Experiment 2, lexicality interacted with the visual quality of the stimulus display, and there was no influence of phonological confusability between the strings being matched. In the divided attention, or multicode, pattern, observed in Experiment 3, lexicality and visual quality produced additive effects, while phonological confusability interfered with different decisions. This suggests that decisions were based on multiple, potentially redundant codes—visual and phonological—and that in such a situation the facilitatory influence of lexicality on visual code formation does not occur. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nonspatial attentional shifts between audition and vision.

This study investigated nonspatial shifts of attention between visual and auditory modalities. The authors provide evidence that the modality of a stimulus (S?) affected the processing of a subsequent stimulus (S?) depending on whether they shared the same modality. For both vision and audition, the onset of S? summoned attention exogenously to its modality, causing a delay in processing S? in a different modality. That undermines the notion that auditory stimuli have a stronger and more automatic alerting effect than visual stimuli (M. I. Posner, M. J. Nissen, & R. M. Klein, 1976). The results are consistent with other recent studies showing cross-modal attentional limitation. The authors suggest that such cross-modal limitation can be produced by simply presenting S? and S? in different modalities and that central processing mechanisms are also, at least partially, modality dependent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of spatial cuing on luminance detectability: Psychophysical and electrophysiological evidence for early selection.

Three experiments were conducted to determine whether attention-related changes in luminance detectability reflect a modulation of early sensory processing. Exps 1 and 2 used peripheral cues to direct attention and found substantial effects of cue validity on target detectability; these effects were consistent with a sensory-level locus of selection but not with certain memory- or decision-level mechanisms. In Exp 3, event-related brain potentials were recorded in a similar paradigm using central cues, and attention was found to produce changes in sensory-evoked brain activity beginning within the 1st 1 msec of stimulus processing. These changes included both an enhancement of sensory responses to attended stimuli and a suppression of sensory responses to unattended stimuli; the enhancement and suppression effects were isolated to different neural responses, indicating that they may arise from independent attentional mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Face preference at birth

Four experiments are reported that were aimed at elucidating some of the controversial issues concerning the preference for facelike patterns in newborns. The experiments were devised to contrast the original and the revised versions of the sensory hypothesis and the structural hypothesis as accounts of face preference in newborns. Experiments 1A and 1B supported the structural hypothesis by showing a visual preference for the stimulus for which components were located in the correct arrangement for a human face. Experiment 2 supported the sensory hypothesis by showing a visual preference for stimuli that were designed to have the optimal spatial frequency components for the newborn visual system. Experiment 3 showed that babies directed attention to a facelike pattern also when it was presented simultaneously with a nonfacelike stimulus with optimal spatial frequency for the newborn visual system.     

Stimulus intensity and the perception of duration.

This article explores the widely reported finding that the subjective duration of a stimulus is positively related to its magnitude. In Experiments 1 and 2 we show that, for both auditory and visual stimuli, the effect of stimulus magnitude on the perception of duration depends upon the background: Against a high intensity background, weak stimuli are judged to last longer. In Experiment 3 we show that the effect of intensity becomes more pronounced at longer durations, consistent with the idea that stimulus intensity affects the pacemaker component of an internal clock, and that it is the difference of a stimulus from the background, rather than its absolute magnitude, which influences the rate of the pacemaker. These results urge a modification to the oft-repeated claim that more intense stimuli seem to last longer, and provide an important constraint on any model of human timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibition of return: Effects of attentional cuing on eye movement latencies.

Inhibition of return refers to a bias against attending to and/or detecting visual stimuli at recently attended locations. A total of 57 Ss participated in 5 experiments, in which Ss were slower to initiate eye movements to previously attended locations. Furthermore, there was more inhibition when a peripheral (exogenous) flash signaled the target, compared with when a central (endogenous) arrow cue was used as an imperative stimulus. That pattern suggests that some of the inhibition is due to processes involved in detecting visual stimuli, and some of the inhibition is related to the movement of the eye. Subsequent experiments showed that the eye-movement component of the inhibition is not object-centered and does not move if the previously attended object moves, although the stimulus-detection component is object-centered. Results have implications for visual attention in general and for the link between overt and covert orienting. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer of noncorresponding spatial associations to the auditory Simon task.

Four experiments examined transfer of noncorresponding spatial stimulus-response associations to an auditory Simon task for which stimulus location was irrelevant. Experiment 1 established that, for a horizontal auditory Simon task, transfer of spatial associations occurs after 300 trials of practice with an incompatible mapping of auditory stimuli to keypress responses. Experiments 2-4 examined transfer effects within the auditory modality when the stimuli and responses were varied along vertical and horizontal dimensions. Transfer occurred when the stimuli and responses were arrayed along the same dimension in practice and transfer but not when they were arrayed along orthogonal dimensions. These findings indicate that prior task-defined associations have less influence on the auditory Simon effect than on the visual Simon effect, possibly because of the stronger tendency for an auditory stimulus to activate its corresponding response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of spatial attention on memory scanning.

Examined the influence of spatial attention on the retrieval of items from short term memory. 48 participants (aged 18–40 yrs) responded to probe letters after sets of 2, 4, and 6 letters were memorized (S. Sternberg, 1966, 1969). Spatial attention was controlled by central arrow cues and stimuli were presented in a clear or a visually degraded form. Overall RT was shorter for attended than for unattended locations, and shorter for clear than for degraded stimuli. Even though the function relating RT to memory-set size for stimuli in attended locations had a significantly smaller zero-intercept than the function for unattended locations, the slope was unchanged, which suggests that attention did not influence the memory-scanning stage. Visual quality interacted with attention, which suggests that they influenced the same stage of processing, presumably the early visual-encoding stage of processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of between-source discriminability on attended and unattended auditory ERPs

Event-related potentials (ERPs) for tone pips from attended and unattended sources, which varied on discriminability, were compared with ERPs for the same stimuli recorded during performance of a visual task. This comparison revealed that Nd, the negative shift of attended relative to unattended ERPs, consisted of three components: a negativity in the attended ERP from 100 to 270 ms, a positivity in the unattended ERP from 170 ms to the end of the epoch, and a second negativity in the attended ERP from 270 to 700 ms. In general, the later onset of early Nd with more difficult between-source discriminations could be attributed to the later onset of the positivity in unattended ERPs. A number of hypotheses were advanced for the origin of the unattended positivity: the suppression of the later of two negative components in the 100-220-ms range, an enhanced P2 component, an endogenous positivity, or the resolution of a protracted negativity elicited by preceding attended stimuli.     

Inhibition and aging: Similarities between younger and older adults as revealed by the processing of unattended auditory information.

The ability to selectively attend to an auditory stimulus appears to decline with age and may result from losses in the ability to inhibit the processing of irrelevant stimuli (i.e., the inhibitory deficit hypothesis; L. Hasher & R. T. Zacks, 1988). It is also possible that declines in the ability to selectively attend are a result of age-related hearing losses. Three experiments examined whether older and younger adults differed in their ability to inhibit the processing of distracting stimuli when the listening situation was adjusted to correct for individual differences in hearing. In all 3 experiments, younger and older adults were equally affected by irrelevant stimuli, unattended stimuli, or both. The implications for auditory attention research and for possible differences between auditory and visual processing are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)