Visual Onset Research Articles

Selective attentional delays and attentional capture among simultaneous visual onset elements.

Visual discrimination and detection responses to a single stimulus presented simultaneously with noise stimuli are slower and less accurate than are responses to a single stimulus presented alone. This occurs even though the location of the relevant stimulus (target) is known or visually indicated with stimuli onset. Results showed that noise elements delay focal attending and processing of a target. Furthermore, precuing the target location reduces, and can eliminate, target processing delays. Processing delays were not due to response competition or to random attentional capture by noise. It is suggested that simultaneous stimuli are perceived initially as a single object, and delays in processing a single stimulus are due to difficulties in perceptually segregating this stimulus from noise. Precuing is assumed to facilitate this segregation process.

Visual motion and attentional capture.

Previous work has shown that abrupt visual onsets capture attention. This occurs even with stimuli that are equiluminant with the background, which suggests that the appearance of a new perceptual object, not merely a change in luminance, captures attention. Three experiments are reported in which this work was extended by investigating the possible role of visual motion in attentional capture. Experiment 1 revealed that motion can efficiently guide attention when it is perfectly informative about the location of a visual search target, but that it does not draw attention when it does not predict the target's position. This result was obtained with several forms of motion, including oscillation, looming, and nearby moving contours. To account for these and other results, we tested a new-object account of attentional capture in Experiment 2 by using a global/local paradigm. When motion segregated a local letter from its perceptual group, the local letter captured attention as indexed by an effect on latency of response to the task-relevant global configuration. Experiment 3 ruled out the possibility that the motion in Experiment 2 captured attention merely by increasing the salience of the moving object. We argue instead that when motion segregates a perceptual element from a perceptual group, a new perceptual object is created, and this event captures attention. Together, the results suggest that motion as such does not capture attention but that the appearance of a new perceptual object does.

Object continuity in apparent motion and attention.

Recent theories of attention have emphasized the role of object-based representations in visual selection. One defining property of any object is spatiotemporal continuity. The present experiments show that the continuity property may underlie two seemingly unrelated perceptual phenomena: attentional capture by abrupt visual onset and the appearance of bistable apparent motion displays. In Experiment 1, observers carried out two visual tasks. In the first task, they reported the appearance of a bistable apparent-motion (or Ternus) display. Whether group or element motion was perceived depended on the duration of the blank interval between successive frames. In the second task, subjects engaged in visual search for a prespecified target, and one each trial one element was briefly flickered off and back on. The degree to which that element captured attention also depended on the duration of the temporal gap. The time course of the gap duration effect in the visual search task was very similar to that for the Ternus display. In Experiment 2, we ruled out the possibility that the presence of an abrupt offset caused the results of Experiment 1. It is argued that the apparent motion and attentional capture phenomena examined here may reflect the operation of the same underlying mechanism: in both cases, a sufficiently long temporal gap disrupts spatiotemporal continuity, thereby fundamentally changing the perceived organization of the display.

Attentional zooming and the global-dominance phenomenon: effects of level-specific cueing and abrupt visual onset.

In four experiments level-specific cueing of hierarchically structured stimuli was used to test the hypothesis that valid cues can reduce the global-dominance phenomenon. Compound stimuli (Experiments 1 and 2) or simple geometric forms (Experiments 3 and 4) were presented with different SOAs after a valid, an invalid, or a neutral level-specific cue (cue validity 80%). Costs for invalid cues and benefits for valid cues were produced in all experiments. However, a reduction of the global-local RT difference to about zero was achieved only after the reduction of the abrupt visual onset accompanying stimulus presentation in Experiments 2 (with compound stimuli) and 4 (with simple geometric forms). In addition, there was no longer the typical asymmetric-interference pattern (i.e., features of the global level interfere with local identification, but not vice versa) that was one of Navon's (1977) main arguments for assuming a perceptual precedence. It is concluded that the RT that is longer for local than for global identifications is produced by the time needed to refocus visual attention intentionally from the global level, which is focussed at first unintentionally, to the local level.

Stimulus-driven attentional capture: evidence from equiluminant visual objects.

Previous work has shown that abrupt visual onsets capture attention. Possible attention. Possible mechanisms for this phenomenon include (a) a luminance-change detection system and (b) a mechanism that detects the appearance of new perceptual objects. Experiments 1 and 2 revealed that attention is captured in visual search by the appearance of a new perceptual object even when the object is equiluminant with its background and thus exhibits no luminance change when it appears. Experiment 3 showed that a highly salient luminance increment alone is not sufficient to capture attention. These findings suggest that attentional capture is mediated by a mechanism that detects the appearance of new perceptual objects.

Figure–ground discrimination from temporal information

The separation of figures from ground is achieved by the visual system based on differences in features such as luminance, colour, depth, orientation, texture or motion. Temporal information, namely phase differences between groups of spatially homogeneous points, can also lead to a clear discrimination of an object shape. The time difference needed to separate figure and ground is around 5 ms over a range of temporal frequencies between 1.3 Hz and 30 Hz, both for sharply focused and for blurred points. These short delays are clearly below the temporal integration time of the visual system. The results have implications for theories on temporal binding and object recognition.

Contingent attentional capture: A reply to Yantis (1993).

Folk, Remington, and Johnston (1992) recently proposed that involuntary shifts of spatial attention, even those elicited by abrupt visual onsets, are contingent on variable internal control settings. Yantis (1993) argues that the results of Jonides and Yantis (1988) significantly challenge this hypothesis and that the paradigm of Folk et al. (1992) is inappropriate for investigating stimulus-driven attentional capture. Yantis's concerns are addressed, and it is concluded that the contingent involuntary orienting hypothesis in fact provides a unified and parsimonious account of the data on attentional capture

Exogenous and endogenous control of attention: The effect of visual onsets and offsets

Two experiments were carried out to investigate the relation between exogenous and endogenous control of visual attention. Subjects searched for a target letter among three nontarget letters that were positioned on an imaginary circle around a fixation point. At different cue-display intervals, a centrally located arrowhead cue reliably indicated the location of the target letter. At different SOAs, a peripheral line segment near one of the letters was either abruptly switched on (Experiment 1) or abruptly switched off (Experiment 2). Presenting the central arrowhead after display onset prevents attention from being focused in advance on the critical location. In this unfocused attentional state, both onset and offset transients attracted attention. When the central arrowhead was available in advance, the focusing of attention prior to display onset precluded attention attraction to the location of the onset or offset transient. Contrary to an offset transient, an onset transient presented at the attended location disrupted performance, indicating that an onset within the spotlight of attention attracts attention. The results are reconciled by means of the zoom-lens theory of attention, suggesting that outside the focus of attention, abrupt transients are not capable of attracting attention. Since the size of the zoom lens is under voluntary control, it can be argued that transients do not fulfill the intentionality criterion of automaticity.

Accuracy of four indirect methods of blood pressure measurement, with hemodynamic correlations

In 38 adults undergoing cardiac surgery, 4 indirect blood pressure techniques were compared with brachial arterial blood pressure at predetermined intervals before and after cardiopulmonary bypass. Indirect blood pressure measurement techniques included automated oscillometry, manual auscultation, visual onset of oscillation (flicker) and return-to-flow methods. Hemodynamic measurements or calculations included heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect and intraarterial blood pressure values were compared by simple linear regression by patient and measurement period. Measurement errors (arterial minus indirect blood pressure) were calculated, and stepwise regression assessed the relationship between measurement error and heart rate, cardiac index, stroke volume index, and systemic vascular resistance index. Indirect to intraarterial blood pressure correlation coefficients varied over time, with the strongest correlations often occurring at the first and last measurement periods (preinduction and 60 minutes after cardiopulmonary bypass), particularly for systolic blood pressure. Within-patient correlations between indirect and arterial blood pressure varied widely--they were consistently high or low in some patients. In other patients, correlations were especially weak with a particular indirect blood pressure method for systolic, mean, or diastolic blood pressure; in some cases indirect blood pressure was inadequate for clinical diagnosis of acute blood pressure changes or trends. The mean correlations between indirect and direct blood pressure values were, for systolic blood pressure: 0.69 for oscillometry, 0.77 for auscultation, 0.73 for flicker, and 0.74 for return-to-flow; for mean blood pressure: 0.70 for oscillometry and 0.73 for auscultation; and for diastolic blood pressure: 0.73 for oscillometry and 0.69 for auscultation. The mean measurement errors (arterial minus indirect values) for the individual indirect blood pressure methods were, for systolic: 0 mm Hg for oscillometry, 9 mm Hg for auscultation, -5 mm Hg for flicker, 7 mm Hg for return-to-flow; for mean: -6 mm Hg for oscillometry, and -3 mm Hg for auscultation; and for diastolic: -9 mm Hg for oscillometry and -8 mm Hg for auscultation. Mean measurement error for systolic blood pressure was thus least with automated oscillometry and greatest with manual auscultation, while standard deviations ranging from 9 to 15 mm Hg confirmed the highly variable nature of single indirect blood pressure measurements. Except for oscillometric diastolic blood pressure, a combination of systemic hemodynamics (heart rate, stroke volume index, systemic vascular resistance index, and cardiac index) correlated with each indirect blood pressure measurement error, which suggests that particular numeric ranges of these variables minimize measurement error.(ABSTRACT TRUNCATED AT 400 WORDS)

Abrupt visual onsets and selective attention: Voluntary versus automatic allocation.

Abrupt visual onsets and selective attention: Voluntary versus automatic allocation.

Abrupt visual onsets and selective attention: Voluntary versus automatic allocation.

The hypothesis that abrupt visual onsets capture attention automatically, as suggested by Yantis and Jonides (1984) was tested in four experiments. A centrally located cue directed attention to one of several stimulus positions in preparation for the identification of a target letter embedded in an array of distractor letters. In all experiments, one stimulus (either the target or one of the distractors) had an abrupt onset; the remaining letters did not. The effectiveness of the cue was manipulated (varying either its duration or its predictive validity) to test whether abrupt onsets capture attention even when subjects are in a highly focused attentional state. Results showed that onsets do not necessarily capture attention in violation of an observer's intentions. A mechanism for partially automatic attentional capture by abrupt onset is proposed, and the diagnosticity of the intentionality criterion for automaticity is discussed.

The control of attention by abrupt visual onsets and offsets.

A letter can be presented visually either by the abrupt appearance of lines that make up the letter (onset transient) or by the abrupt disappearance of extra lines from a form in which the letter is embedded (offset transient). Recent evidence from visual-search tasks has suggested that onset transients have absolute priority over offset transients with respect to the allocation of visual attention. Specifically, these studies have found that a single onset-transient target letter pops out of a background of offset-transient distractor letters (i.e., time to detect the target is independent of the number of distractors), which indicates that attention is automatically directed to the location of an onset-transient stimulus even when there are competing offset transients (Yantis & Jonides, 1984). Because of the way the offset letters were created, however, the total display change (number of offset line-segments plus number of onset line-segments) was greater for onset than for offset letters. Thus, onset targets might have popped out because they produced greater overall display changes rather than because they were the only letters with onset transients. In the present study, a figure that included more offset-transient line segments in the offset-transient letters was used. Under these conditions, onset-transient targets did not pop out of a background of offset-transient distractors. It is suggested that visual attention may be influenced by total display change and, therefore, that onset transients are not necessarily sufficient to control attention when there are many competing offset transients.

Developmental regulation of sterol biosynthesis inCucurbita maxima L.

AbstractTwenty‐two sterols were identified by capillary gas chromatography and capillary gas chromatography/mass spectroscopy inCucurbita maxima grown under green‐house conditions. Both whole plants and individual tissues (leaves, stems, roots, cotyledons, flowers) were analyzed at weekly intervals during the 12‐week development of the plant. In whole plants, sterol accumulation parallels plant growth except for a period in the mid‐life cycle where there is a reduction in the amount of sterol accumulated on a total sterol/plant and mg sterol/g dry wt basis. This reduction in the amount of sterol is coincident with the visual onset of flowering. During development, the percent contribution of each class of sterol (Δ5_, Δ7_, Δ0_‐sterols) remains relatively constant. However, the percent contribution of an individual sterol species varies depending on the tissue examined and the developmental period selected for analysis. While the young plant (<2 weeks) possesses elevated levels of sterols with the Δ25(27)‐double bond, the trend was toward a reduction in the amounts of these sterols with development. Leaves and stems accumulate large quantities of 24ζ‐ethyl‐5α‐cholesta‐7,22‐dien‐3β‐ol (7,22‐stigmastadienol) and 24ζ‐ethyl‐5α‐cholest‐7‐en‐3β‐ol (7‐stigmastenol), while roots accumulate only 7,22‐stigmastadienol as their principal sterol. Male flowers and roots were found to contain elevated levels of Δ5_‐sterols.

The effects of monocular deprivation on the visual latency of geniculate X- and Y-cells in the cat.

Monocular lid suture deprivation during early visual development of the cat alters the temporal flow of retinal information as it passes through the dorsal lateral geniculate nucleus. The latencies of Y-cells located in the deprived layers and of both X- and Y-cells in the non-deprived layers are shorter than the latencies of their counterparts in normally reared cats. The visual response onset latencies of X-cells located in the deprived geniculate layers lag those of X-cells in the non-deprived layers.

Abrupt visual onsets and selective attention: Evidence from visual search.

Abrupt visual onsets and selective attention: Evidence from visual search.

Abrupt visual onsets and selective attention: evidence from visual search.

The effect of temporal discontinuity on visual search was assessed by presenting a display in which one item had an abrupt onset, while other items were introduced by gradually removing line segments that camouflaged them. We hypothesized that an abrupt onset in a visual display would capture visual attention, giving this item a processing advantage over items lacking an abrupt leading edge. This prediction was confirmed in Experiment 1. We designed a second experiment to ensure that this finding was due to attentional factors rather than to sensory or perceptual ones. Experiment 3 replicated Experiment 1 and demonstrated that the procedure used to avoid abrupt onset--camouflage removal--did not require a gradual waveform. Implications of these findings for theories of attention are discussed.

Latencies for chromatic and achromatic visual mechanisms

Relative visual onset latency and offset latency (visual persistence) were measured (using perceived simultaneity methodsl for pulsed chromatic stimuli presented under two conditions: as luminance increments of 0.2 or 0.3 log unit above a prevailing achromatic background field, or in hue substitution, matched in luminance to the achromatic field so as to eliminate spatio-temporal luminance transients. In the first experiment, for the hue substitution condition, both onset and offset latencies were found to be slow relative to latencies for the increment condition, and varied with wavelength according to a function resembling trichromatic saturation discrimination (slowest latency at 570 nm). Latencies to increment pulses of equal luminance did not vary with wavelength. In a second experiment, offset latency was measured as a function of pulse duration and pulse luminance level. The observed decrease in offset latency with pulse duration was markedly steeper at short pulse durations for chromatic increments than for hue substitution stimuli. Offset latency decreased with increasing pulse luminance for incremental stimuli but not for hue substitution stimuli. These results are interpreted as reflecting the temporal response properties of chromatic neural mechanisms (the hue substitution data) and the achromatic mechanism (the increment data).

Transient and impulse responses of a one-dimensional linearly attenuating medium -- II. A parametric study

We investigate one-dimensional waves in a standard linear solid for geophysically relevant ranges of the parameters. The critical parameters are shown to be T*= t_u/Q_m where t_u is the travel time and Q_m the quality factor in the absorption band, and τ^(-1)_m, the high-frequency cut-off of the relaxation spectrum. The visual onset time, rise time, peak time, and peak amplitude are studied as functions of T* and τ_m. For very small τ_m, this model is shown to be very similar to previously proposed attenuation models. As τ_m grows past a critical value which depends on T*, the character of the attenuated pulse changes. Seismological implications of this model may be inferred by comparing body wave travel times with a ‘one second’ earth model derived from long-period observations and corrected for attenuation effects assuming a frequency independent Q over the seismic band. From such a comparison we speculate that there may be a gap in the relaxation spectrum of the Earth's mantle for relaxation times shorter than about one second. However, observational constraints from the attenuation of body waves suggest that such a gap might in fact occur at higher frequencies. Such a hypothesis would imply a frequency dependence of Q in the Earth's mantle for short-period body waves.

A source of bias in multiple ScS differential travel times determined by waveform correlation

Differential travel times determined by waveform correlation techniques between seismic phase pairs suffer an inherent systematic bias with respect to conventional visual timing methods if the phase pairs have different attenuation histories. Synthetic shear waves are generated with attenuation histories appropriate for multiple ScS waves. The bias between the ScS2‐ScS differential time determined by visual onset and a differential time picked by waveform cross‐correlation ranges between 2.2 and 3.8 seconds late, for an assumed average Qβ of the mantle of 312 and 156, respectively. Corrections are calculated for the various ScSn−ScSn−1 phase pairs for a range of ScS t* values.

Probe electric field measurements near a midlatitude ionospheric barium release

A double-probe measurement of midlatitude ionospheric electric fields was made on a rocket flight near a large, artificial, barium plasma cloud. The measurement was made after ground sunset on February 1, 1971, near L = 1.8, 7 min after the release of the barium and 4 min before the visual onset of its striations. The cloud-associated perturbation of the approximately 4-mv/m electric field in an earth-fixed frame of reference was in agreement with theoretical expectations based on the enhancement of the Pedersen conductivity produced by the cloud and lends support to the gradient drift instability model of striation formation. The motion of the leading edge of the barium cloud was consistent with that expected from the rocket electric field measurement. The ionospheric electric field in a frame of reference not rotating with the earth differed from the corotation electric field by about 20% during the flight.