Don R. Lyon

Central and peripheral precuing of forced-choice discrimination

There are suggestions in the literature that spatial precuing of attention with peripheral and central cues may be mediated by different mechanisms. To investigate this issue, data from two previous papers were reanalysed to investigate the complete time course of precuing target location with either: (1) a peripheral cue that may draw attention reflexively, or (2) a central, symbolic cue that may require attention to be directed voluntarily. This analysis led to predictions that were tested in another experiment. The main result of this experiment was that a peripheral cue produced its largest effects on discrimination performance within 100 msec, whereas a central cue required approximately 300 msec to achieve maximum effects. In conjunction with previous findings, the present evidence for time differences between the two cuing conditions suggests that more than one process is involved in the spatial precuing of attention.

A framework for understanding the allocation of attention in location-precued discrimination

The effects of attention on visual perception are assessed in the location-precuing paradigm. First, we present a review of some current metaphors for attention and relevant data. Then, a framework is suggested that provides an interpretation of the temporal sequence of external and assumed internal processes within a location-cuing trial. Cases when a precue correctly indicates the target location (valid trials) are compared to cases when the precue directs attention to the wrong location (invalid trials) with the cue location either at fixation or peripheral to the target location. Several specific hypotheses are suggested; these concern decrements in performance on invalid trials and effects of the location of a precue. For the most part, these hypotheses are supported by data in the literature and in some new studies. A gradient-filter metaphor for attention, which includes a synthesis of ideas from the gradient model and the attention gate model, is more consistent with the data than is a spotlight metaphor.

Attention Effects on Form Discrimination at Different Eccentricities

Considerable disagreement exists in the visual attention literature about how attention is allocated over the visual field. One frequently expressed metaphor is that attention moves like a spotlight, and in some variants it is assumed that attention takes longer to shift to targets further from fixation. In order to test this metaphor, five experiments were conducted in which target location was precued and form discrimination accuracy was assessed. By varying the interval between the precue and the target (stimulus onset asynchrony, SOA), a time course of attention effects was obtained for targets at 2°, 6°, and 10° eccentricity. In the first three experiments, precueing effects were found, but there were no differences in performance as a function of eccentricity for very short SOAs, with either a peripheral cue or a foveal arrow cue. For long SOAs, however, performance was better for targets that were closer to fixation. In Experiments 4 (peripheral cue) and 5 (foveal cue), the targets were scaled to make them equally discriminable at all eccentricities. Again precueing effects were found, but there were no differences in accuracy as a function of eccentricity for most SOAs. These results suggest that attention shifting is not analogous to a constant-velocity moving spotlight.

Attention in visual search: Multiple search classes

Data from visual-search tasks are typically interpreted to mean that searching for targets defined by feature differences does not require attention and thus can be performed in parallel, whereas searching for other targets requires serial allocation of attention. The question addressed here was whether a parallel-serial dichotomy would be obtained if data were collected using a variety of targets representing each of several kinds of defining features. Data analyses included several computations in addition to search rate: (1) target-absent to target-present slope ratios; (2) two separate data transformations to control for errors; (3) minimum reaction time; and (4) slopes of standard deviation as a function of set size. Some targets showed strongly parallel or strongly serial search, but there was evidence for several intermediate search classes. Sometimes, for a given target-distractor pair, the results depended strongly on which character was the target and which was the distractor. Implications from theories of visual search are discussed.

Does attention have different effects on line orientation and line arrangement discrimination

Visual search and texture segregation studies have led to the inference that stimuli differing in the orientation of their component line segments can be distinguished without focal attention, whereas stimuli that differ only in the arrangement of line segments cannot. In most of this research, the locus of attention has not been explicitly manipulated. In the first experiment presented here, attention was directed to a relevant peripheral target by a cue presented near the target location or at the fovea. Effects of attention on orientation discrimination were assessed in a two-alternative forced-choice task with targets that were either: (1) lines that slanted obliquely to the right or left, or were horizontal or vertical, or (2) Y-like targets that had a short arm leading obliquely right or left of a vertical line. In some groups, a four-alternative forced-choice test with lines at 0°, 45°, 90°, and 135° orientations was used. Discrimination of these targets (i.e. targets that differ in the orientation of component line segments) was only minimally facilitated as the time between the onset of the valid cue and the onset of the target (cue-target stimulus onset asynchrony, SOA) was increased from 0 or 17 msec to 267 msec. In contrast, discrimination of targets that did not differ in the orientation of component line segments but differed in line arrangement (T-like characters), was greatly facilitated by longer cue-target SOAs. In Experiment 2, a cue misdirected attention on 20% of the trials. A decrement occurred on incorrectly cued trials in comparison to correctly cued trials for both types of stimuli used (lines and Ts). The results from these experiments suggest that discrimination of line orientation benefits less from focal attention than does discrimination of line arrangement, but that both discriminations suffer when attention must be disengaged from an irrelevant spatial location.

Importance of precue location in directing attention

In location-precuing experiments, accuracy in discrimination of T-like characters improves with increasing time between the precue and the target. In this experiment, two central and two peripheral cue locations were examined using 13 different cue-target intervals from 0 to 234 msec. Accuracy was the same when trials were cued from the two peripheral locations (two thirds distance between fixation and target or distal to the target location). Centrally cued trials (cues at fixation or next to fixation) resulted in slower onset of attentional effects than peripherally cued trials, but there was greater accuracy at long cue-target intervals for central than for peripheral cues. Data are compared to previously published research.

Benefits from attention depend on the target type in location-precued discrimination

In previous research, we found that precuing of attention to a target location greatly improved discrimination of targets that differed in line arrangement, but had little effect on discrimination of targets that differed in line orientation. In the present research, a number of other targets that represent various feature differences were used. The new data are consistent with and extend our earlier findings by showing that (1) there is some effect of precuing with all targets tested, and (2) the size of precuing effects varies in a complex way with the nature of the target. Moreover, the difficulty of the discrimination cannot explain the size of the precuing effects. A framework for understanding the events occurring during trials in the location-cuing paradigm is presented and applied to these results.

Inhibition of Return in Visual Identification Tasks

In detection tasks, at long precue-target intervals, inhibition from precueing, rather than facilitation, has been shown. This inhibition, called “inhibition of return” (IOR), does not always occur in discrimination or identification tasks. Here in post-hoc analyses and three new experiments, evidence for IOR was shown in a target identification task using a location-cueing paradigm. In Experiments 1 and 2, a series of three cues attracted attention without eye movement, first to one of four peripheral locations, then to fixation, and then either back to the initial location or to a different one. Identification accuracy for masked visual targets was impaired when third-cue and first-cue locations matched, which constitutes evidence forIOR. In Experiment3, there was no third cue. An uninformative first cue was followed by a cue at fixation, and then a peripheral target in a “go/no-go” reaction time task. Inhibition of return was still obtained. Thus, IOR can affect identification as well as detection perf...

Attention and nontarget effects in the location-cuing paradigm.

Three experiments were conducted in order to determine whether irrelevant items presented outside the focus of attention would affect the identification of a precued target. A peripheral cue indicated one of eight possible locations in a circular array, centered on fixation with a radius of 5.25°. After a variable interval (0–200 msec), eight characters were presented briefly and masked. In each experiment, there was an effect of the identity of the characters at the seven noncued locations (the nontargets) on the accuracy of identification of the target. When there were more nontargets identical to the target, accuracy was higher than when there were fewer nontargets identical to the target. Nontargets consistently affected performance despite incentives to focus only on the target.

Time Course of Location-Cuing Effects With a Probability Manipulation

A location-cuing paradigm was used to study the effects of cue probability on the allocation of visual attention. A cue was used to indicate the likely location of a target (out of 4 possible target locations), with 8 cue-target onset intervals, ranging from 0 to 233 ms. There were 3 blocked proportions of correctly cued trials, 100%, 75%, and 50%. The observers had higher target discrimination accuracy at highly probable locations than at less probable locations, and these differences were maintained across all cue-target onset intervals. Thus, it appeared that the observers were allocating attention as a function of cue probability, with a consistent pattern throughout the time course of the development of attention. The consistent pattern across stimulus onset asynchronies (SOAs) suggests that the effects of time after cue and the effects of probability may rely on independent processes.