Biomedical subjects

Jay Pratt

Publications and source records attributed to Jay Pratt.

At least 37 records · Page 2Linked to original sources

PubMed2004

An illusion of 3-D motion with the Ternus display.

We attempted to eliminate the percept of element motion in the Ternus display by connecting the display elements so that they appeared to be a single object. On each trial, the display elements (two discs) appeared either separated or connected (either via a white line or side by side) and subjects reported whether they observed element motion or group motion at various ISIs. Although it was hypothesized that element motion would be eliminated in the connected condition, subjects observed element motion at short ISIs in the form of a three dimensional illusion in which one element appeared to rotate out in front of (or behind) the other. Implications for short range and long range motion processes are discussed.

Adult↗

PubMed2004

Examining inhibition of return with onset and offset cues in the multiple-cuing paradigm.

Three experiments examined inhibition of return (IOR) with onset and offset cues in a multiple-cuing paradigm. In the first two experiments, five sequential cues either appeared and remained present (onset cues) or disappeared and remained absent (offset cues). In the third experiment, the cues were either onset cues or on-off cues (appeared and then disappeared quickly after). With placeholders present, onset and offset cues produced similar declines in IOR from the most recently cued location (Experiment 1). In contrast, onset cues produced overall more IOR than on-off cues (Experiment 3). With placeholders absent (Experiment 2), no IOR was found for either onset or offset cues. The results suggest that even in a complex multiple-cuing paradigm, onsets and offsets are treated similarly by the attentional system. Furthermore, it appears that onset cues are easier to encode as previously searched than on-off cues, suggesting a role of working memory in IOR. Finally, when multiple locations are cued sequentially by onsets and offsets they must be marked by placeholders for inhibition to occur.

Attention↗

PubMed2004

The role of temporal and spatial factors in the covert orienting of visual attention tasks.

There is a biphasic pattern in response times to peripheral uninformative cues, with faster responses to targets in cued locations when the stimulus onset asynchrony (SOA) is under 300 ms and slower responses when it is over 300 ms. The effect has typically been attributed entirely to the SOA while ignoring other aspects of the cues (duration, spatial configuration). To examine these other factors, along with SOA, the present experiments included manipulations of SOA (50, 100, 200, 400, 800 ms), inter-stimulus interval (ISI; 0, 50, 100, 150, 200, 300, 350, 400, 500, 600, 700, and 750 ms), and whether or not the cue and target overlap in the same space. The results indicate that cueing effects depend on the combination of cue duration, ISI, SOA, and the spatial configuration of the cues and targets. Three factors are used to explain these time course results.

Analysis of Variance↗

PubMed2004

The planning and execution of sequential eye movements: saccades do not show the one target advantage.

The present experiment examined the one-target advantage (OTA) with regard to saccadic eye movements. The OTA, previously found with manual pointing responses, refers to the finding that movements are executed faster when the limb is allowed to stop on the target compared to the situation where it has to proceed and hit a second target. Using an adapted limb movement OTA task, saccades of 5 degrees and 15 degrees were made to (a) a single target (one-target), (b) one target and immediately to another target without a change in direction (two-target-extension), and (c) one target and immediately back to the start location (two-target-reversal). Unlike manual movements, the movement times for the initial saccade in the two-target-extension condition were not prolonged compared to either of the other two conditions. Moreover, this pattern of results was found for both the shorter and longer amplitude saccades. The results indicate that the OTA does not occur in the oculomotor system and therefore is not a general motor control phenomenon.

Hand↗

PubMed2004

The influence of distractor-only prime trials on the location negative priming mechanism.

Two experiments were conducted that examined the influence of distractor-only prime trials on the "location" negative priming (NP) effect. In all experiments, the probe trial always lacked a distractor. We showed that the predictable absence of a probe distractor caused the elimination of the location NP effect when the prime trial contained both a target and a distractor event (T + D-->T), but not when the prime contained only a to-be-ignored distractor event (D-->T) (Milliken, Tipper, Houghton, & Lupianez, 2000). The preservation of the NP effect seen with the distractor-only prime trials (D-->T) was not the result of its lacking a prime-trial selection, nor was it the consequence of its representing a higher level of episodic similarity than the T + D-->T condition. Finally, the location NP effect observed for the D-->T condition is seemingly consistent with the view that location NP and the inhibition-of-return effects share a common underlying process (Milliken et al., 2000).

Adult↗

PubMed2004

Dissociating visual attention and effector selection in spatial precuing tasks.

In this study the authors tested and rejected a recent proposal that response precuing effects depend on the spatial extent of the precues rather than on the number of response choices. Moreover, the authors tested and supported the hypothesis that the number of effectors in the response set is an important determinant of spatial precuing effects. Results of 4 experiments consistently showed that keypress responses generated a qualitatively different pattern of precuing effects than did pointing and detection responses. Together, the results establish a strong dissociation between planning pointing responses and planning keypress responses and suggest that precuing effects in 1-effector and multiple-effector visuomotor tasks are dominated by distinct and separate mechanisms, visual attention and effector selection, respectively.

Adolescent↗

PubMed2004

Object-based processes in the planning of goal-directed hand movements.

Theories in motor control suggest that the parameters specified during the planning of goal-directed hand movements to a visual target are defined in spatial parameters like direction and amplitude. Recent findings in the visual attention literature, however, argue widely for early object-based selection processes. The present experiments were designed to examine the contributions of object-based and space-based selection processes to the preparation time of goal-directed pointing movements. Therefore, a cue was presented at a specific location. The question addressed was whether the initiation of responses to uncued target stimuli could benefit from being either within the same object (object based) or presented at the same direction (space based). Experiment 1 replicated earlier findings of object-based benefits for non-goal-directed responses. Experiment 2 confirmed earlier findings of space-based benefits for goal-directed hand pointing movements. In Experiments 3 and 4, space-based and object-based manipulations were combined while requiring goal-directed hand pointing movements. The results clearly favour the notion that the selection processes for goal-directed pointing movements are primarily object based. Implications for theories on selective attention and action planning are discussed.

Attention↗

PubMed2004

Competing top-down processes in visual selection: evidence that selection by location is stronger than selection by color.

The purpose of this study was to examine whether color and position information are functionally equivalent when observers are asked to select simultaneously on both dimensions. Observers were asked to report a letter of a given color from a given region of a briefly flashed letter array, then to report any additional letters they could recall from the stimulus set. Of the additional letters, more location letters were reported than were same-color or neutral letters. The results suggested that position information has priority over color information in top-down-guided visual selection.

Color Perception↗

PubMed2004

A new estimation of the duration of attentional dwell time.

How rapidly can attention move from one object to the next? Previous studies in which the dwell time paradigm was used have estimated attentional switch times of 200-500 msec, results incompatible with the search rate estimates of 25-50 msec shown in numerous visual search studies. It has been argued that dwell times are so long in the dwell time paradigm because the attentional shifts measured are unlike those used in visual search. In the present experiment, a variation of a visual search task was used, in which serial endogenous (volitional) deployments of attention were measured directly by means of a probe reaction time task. The experiment revealed a dwell time of about 250 msec, consistent with the faster estimates from other dwell time studies. This result suggests that endogenous shifts of attention may be relatively slow and that the faster attentional shifts estimated from visual search tasks may be due to the involvement of bottom-up processes.

Attention↗

PubMed2004

Illusory gravitational forces affect aimed limb movements.

The authors report on 2 experiments in which participants produced rapid wrist-rotation movements in a clockwise direction to move a cursor from a home position into a target region. The display was constructed such that the target could be depicted above, below, or beside the home position, so that the clockwise wrist rotation could produce upward, downward, or rightward movements of the cursor. By parsing the movements into component submovements, the authors found that upward movements were consistently less forceful, as evidenced by shorter primary submovements, compared with downward and horizontal movements. Those results suggested a new virtual gravity illusion: Participants apparently overcompensated for the absence of the anticipated effects of gravity by adjusting the initial force they used to propel the cursor toward the target.

Adult↗

PubMed2003

The attentional repulsion effect in perception and action.

The attentional repulsion effect refers to the perceived displacement of a Vernier stimulus in a direction that is opposite to a brief peripheral cue. The twofold purpose of the present study was to: (1) replicate the perceptual effect using a Vernier discrimination task, and (2) determine whether the effect would also affect action using a guided localization task. A perceptual attentional repulsion effect was found in experiment 1 and a similar effect was found in experiment 2, with a computer mouse localization task, and in experiment 3, with a guided limb localization task (in both cases pointing responses were biased in the direction opposite to that of the cue). These findings suggest that the attentional repulsion effect occurs early in visual processing, probably affecting the receptive fields of the position-coding units in primary visual cortex before "object-perception" and "object-action" information is segregated into separate pathways.

Analysis of Variance↗

PubMed2003

Examining the time course of facilitation and inhibition with simultaneous onset and offset cues.

The experiment conducted examined the effect of simultaneously presented onset and offset cues on the orienting of attention in the visual field. Subjects were presented with a display that consisted of four placeholder boxes around a central fixation point. An onset and an offset cue appeared simultaneously in two of the locations, and the other two locations provided a neutral baseline condition. Reaction times were measured in a simple target detection task with stimulus-onset asynchronies (SOAs) that ranged from 100 ms to 1,000 ms. As expected, the onset cue produced early facilitation and later occurring inhibition of return (IOR). The offset cue produced significant inhibition at all but the earliest SOA. These results suggest that simultaneously presented onset and offset cues both capture attention, but that attention is rapidly disengaged from the location of the offset cue, resulting in earlier occurring IOR. For the onset cues, attention is allocated for a longer period of time, producing the typical pattern of early facilitation and later occurring IOR. The differing time course of attention at each location may reflect separate facilitatory and inhibitory processes, and the priority given to the onset of a stimulus by the attentional system.

Attention↗

PubMed2003

Symbolic control of visual attention: The role of working memory and attentional control settings.

This study examined how 1 symbol is selected to control the allocation of attention when several symbols appear in the visual field. In Experiments 1-3, the critical target feature was color, and it was found that uninformative central arrows that matched the color of the target were selected and produced unintentional shifts of attention (i.e., involuntary, initiated slowly, producing long-lasting facilitatory effects). Experiment 4 tested whether such selection is the result of an attentional filter or of a competition bias due to a match of incoming information against integrated object representations stored in working memory. Here, the critical feature was shape and color was irrelevant, but matching color arrows were still selected. Thus, features of objects in working memory will bias the selection of symbols in the visual field, and such selected symbols are capable of producing unintentional shifts of attention. ((c) 2003 APA, all rights reserved)

Adult↗

PubMed2003

Perceiving numbers causes spatial shifts of attention.

Number symbols are part of our everyday visual world. Here we show that merely looking at numbers causes a shift in covert attention to the left or right side, depending upon the number's magnitude. This observation implies obligatory activation of number meaning and signals a tight coupling of internal and external representations of space.

Attention↗

PubMed2003

Adult age differences in the time course of inhibition of return.

Inhibition of return (IOR) occurs when people are slower to detect a target that appeared at a previously cued location. Prior research has shown that younger and older adults display similar amounts of IOR, but this research has not examined the time course of the process. Because elderly people may be slower to engage or disengage spatially based attention, the present experiment examined age differences in IOR at stimulus-onset asynchronies ranging from 50 ms to 3,000 ms. The results show that the peak magnitude of IOR was similar for younger and older adults, but the onset of IOR occurred approximately 300 ms later in elderly persons. Older adults also showed a greater degree of facilitation at shorter stimulus-onset asynchronies. The results suggest that there is a change in the temporal dynamics of inhibition that occurs with age.

Adult↗

PubMed2003

Inhibition of return and manual pointing movements.

To examine whether the motor inhibition of return (IOR) postulated by Taylor and Klein (1998, 2000) generalizes to manual guided movements or is restricted to saccadic responses, the following three experiments were conducted. The first experiment combined peripheral cues (which generate IOR) with four types of manual responses made to central targets (central arrow indicating the response location). The responses were made on a touch-screen and were the equivalent of either a detection keypress, a choice keypress, a detection-guided pointing movement, or a choice-guided pointing movement. No IOR was found for any of the responses. The second experiment replicated the main result under eye fixation control. In Experiment 3, peripheral cues and peripheral targets were used, and IOR was present in all responses. Overall, these finding suggest that motor-based IOR is restricted to the oculomotor system. Implications for motor-based IOR and attention-based IOR are discussed.

Adult↗

PubMed2003

The role of spatial working memory in inhibition of return: evidence from divided attention tasks.

Inhibition of return (IOR) refers to a bias against returning attention to a location that has been recently attended. In the present experiments, we examined the role of working memory in IOR by introducing secondary tasks (in the temporal interval between the cue and the target) that involved a working memory component. When the secondary task was nonspatial in nature (monitoring odd digits or adding digits), IOR was present, although overall reaction times were greater in the presence of the secondary task. When the task involved a spatial working memory load (remembering the directionality of arrows or the orientation of objects), IOR was eliminated. However, when the participants had incentive to process the directionality of an arrow but did not have to use any memory system, IOR persisted at peripheral locations. Overall, the results suggest that IOR is partially mediated by a spatial working memory system.

Attention↗

PubMed2003

Inhibition of return with rapid serial shifts of attention: implications for memory and visual search.

Horowitz and Wolfe (2001) suggested that inhibition of return (IOR) should not be observed in tasks that involve rapid deployments of attention. To examine this issue, five of six possible locations were sequentially cued with either short-duration peripheral cues (50 msec) or long-duration peripheral cues (500 msec). As was expected, IOR was observed in the first two experiments at every cued location with the long-duration cues, with the magnitude of IOR decreasing for earlier cued locations relative to later cued locations. In the short-cue condition, IOR was observed at only one cued location (the second to last). The pattern of results for the short-duration cues was found regardless of whether the fixation cue was of a short (Experiment 1) or a long (Experiment 2) duration. In Experiment 3, the final fixation cue was removed, and IOR was again observed at virtually all locations in both the short- and the long-cue conditions. These findings indicate that IOR can be observed at multiple locations when attention is shifted rapidly between locations.

Attention↗