Biomedical subjects

S P Tipper

Publications and source records attributed to S P Tipper.

At least 19 recordsLinked to original sources

PubMed2000

Impaired distractor inhibition on a selective attention task in unmedicated, depressed subjects.

BACKGROUND: Impaired distractor inhibition may contribute to the selective attention deficits observed in depressed patients, but studies to date have not tested the distractor inhibition theory against the possibility that processes such as transient memory review processes may account for the observed deficits. A negative priming paradigm can dissociate inhibition from such a potentially confounding process called object review. The negative priming task also isolates features of the distractor such as colour and location for independent examination. METHOD: A computerized negative priming task was used in which colour, identification and location features of a stimulus and distractor were systematically manipulated across successive prime and probe trials. Thirty-two unmedicated subjects with DSM-IV diagnoses of non-psychotic unipolar depression were compared with 32 age, sex and IQ matched controls. RESULTS: Depressed subjects had reduced levels of negative priming for conditions where the colour feature of the stimulus was repeated across prime and probe trials but not when identity or location was the repeated feature. When both the colour and location feature were the repeated feature across trials, facilitation in response was apparent. CONCLUSIONS: The pattern of results supports studies that found reduced distractor inhibition in depressed subjects, and suggests that object review is intact in these subjects. Greater impairment in negative priming for colour versus location suggests that subjects may have greater impairment in the visual stream associated with processing colour features.

Adolescent↗

PubMed2000

Attending, ignoring, and repetition: on the relation between negative priming and inhibition of return.

A series of spatial localization experiments is reported that addresses the relation between negative priming and inhibition of return. The results of Experiment 1 demonstrate that slowed responses to repeated location stimuli can be obscured by repetition priming effects involving stimulus dimensions other than spatial location. The results of Experiments 2, 3A, and 3B demonstrate that these repetition priming effects may occur only when participants are required to respond to the prime display. Together, these results suggest that differences between attended and ignored repetition effects in selective attention studies of spatial localization do not provide a basis for distinguishing between spatial negative priming and inhibition of return.

Adult↗

PubMed1999

Attention accesses multiple reference frames: evidence from visual neglect.

Research with normal participants has demonstrated that mechanisms of selective attention can simultaneously gain access to internal representations of spatial information defined with respect to both location- and object-based frames of reference. The present study demonstrates that patients with unilateral spatial neglect following a right-hemisphere lesion are poorer at detecting information on the contralateral left side in both location- and object-based spatial coordinates simultaneously. Moreover, the extent of the neglect is modulated by the probability of a target's appearing in either reference frame; as the probability of sampling a target in a particular frame of reference increases, so does the severity of neglect in the frame. These findings suggest that attention can be flexibly and strategically assigned to a reference frame depending on the contingencies of the task.

Aged↗

PubMed1999

Inhibition of return in a selective reaching task: an investigation of reference frames.

Most previous studies of inhibition of return (IOR) have examined reaction time (RT) and accuracy. These effects have been observed via saccades to targets or with key-press responses. In this study the authors examined, for the first time, IOR in components of a selective reaching task in which participants directly reached for and depressed target keys. When the interval between cue and target was 600 ms, robust IOR effects were observed in RT to begin the reach, but no effects were observed in the movement components (movement time to complete the reach and the path of the reach). However, when the cue-target interval was short (200 ms), hand paths deviated toward the cue. The results suggest that although RT measures of IOR appear to reveal perceptual rather than action-based processes, action-based representations may be briefly activated by irrelevant cues, which can be observed via analysis of three-dimensional reach path.

Adolescent↗

PubMed1999

Scene-based and object-centered inhibition of return: evidence for dual orienting mechanisms.

We investigated whether inhibition of return (IOR) could be observed in location-based, scene-based, and object-centered frames of reference. IOR was found to move both with a separate cued object (scene-based) and with a location within a single rotating object (object-centered). Importantly, however, IOR was also associated with the environmental location cued when cuing was of a separate object (scene-based), whereas facilitation of the cued location was found when cuing was of a component within an object. These results suggest that location is of central importance to scene-based representations of separate objects, which appear to be encoded in viewer-centered coordinates, whereas environmental locus is of little relevance when attention orients within a single object. The results also provide further evidence for the coexistence of both excitation and inhibition associated with uninformative exogenous cues.

Adult↗

PubMed1998

Action-based mechanisms of attention.

Actions, which have effects in the external world, must be spatiotopically represented in the brain. The brain is capable of representing space in many different forms (e.g. retinotopic-, environment-, head- or shoulder-centred), but we maintain that actions are represented in action-centred space, meaning that, at the cellular level, the direction of movement is defined by the activity of cells. In reaching, for example, object location is defined as the direction and distance between the origin of the hand and the target. Most importantly, we argue that more than one task-relevant action can be evoked at any moment in time. Therefore, highly efficient selection processes that accurately link vision and action have had to evolve. Research is reviewed which supports the notion of action-based inhibitory mechanisms that select the target from competing distractors.

Animals↗

PubMed1998

Vision influences tactile perception without proprioceptive orienting.

The perception of tactile stimuli is facilitated when subjects look towards the stimulated body site: this facilitation even takes place when visual information is unavailable, as when orienting in the dark. It is not known whether the facilitation is due entirely to such proprioceptive orienting of eye and head, or whether visual information of the body site can also facilitate touch. An experiment is reported which dissociates vision and proprioception, and demonstrates for the first time that vision of a body part, independent of proprioceptive orienting, can indeed effect somatosensation.

Adult↗

PubMed1998

Priming reveals attentional modulation of human motion sensitivity.

Although recent fMRI and single unit recording studies have shown that attention modulates neural activity in motion sensitive areas of extrastriate cortex, these approaches cannot reveal qualitative or quantitative effects of attention on perception of motion. To investigate this, we asked observers to select one of two orthogonal directions in a brief, transparent dot display (prime) and then measured their sensitivity to global directional motion in a second uni-directional dot display (probe) presented a short time later. When probe direction matched the attended prime direction, sensitivity was degraded. But, when probe direction matched the ignored prime direction, sensitivity was enhanced, even though both components were of equal physical strength. Sensitivity was unchanged for directions opposite to either previously seen direction. Neither sensory adaptation nor opponent direction mechanisms can account for these data. Rather, processes initiated by visual selection must underlie these dramatic changes in motion sensitivity.

Adaptation, Psychological↗

PubMed1998

Reaching into cluttered visual environments: spatial and temporal influences of distracting objects.

Subjects reached for visual target lights in the presence of distractor lights. Previous studies (e.g., Tipper, Lortie, & Baylis, 1992) have shown that distractors at locations between the starting position of the hand and the target location caused greater interference (as indexed by response time) than distractors beyond the target. This finding has been attributed to the former distractors being in the path of the response to the target, but we provide evidence that they interfere more because of their proximity to the starting position of the hand (a "proximity-to-hand effect"). Also, distractors located in the hemispace ipsilateral to the responding hand caused more interference than contralateral distractors (an "ipsilateral effect"). The proximity-to-hand and ipsilateral effects were found in both reaction and movement time, suggesting that the resolution of the selection problem caused by a distractor could occur before or after movement initiation. Further evidence for this suggestion was provided by individual differences in movement initiation strategies which were predictive of the temporal locus of distractor influence. Errors of touching the distractor location also showed proximity-to-hand and ipsilateral effects. We discuss applications of these findings to real-world situations in which people reach for the wrong object in multiple-object visual displays.

Adult↗

PubMed1997

Hand deviations away from visual cues: indirect evidence for inhibition.

Previous research has demonstrated that when a stimulus is to be ignored, the path of motion towards a target (saccade or manual reach) deviates away from the to-be-ignored stimulus. Path deviations in saccade and reaching tasks have, however, been observed in very different situations. In the saccade tasks subjects initially attended to a cue, then disengaged attention while saccading to a target. By contrast, in the selective reaching tasks attention was continuously withdrawn from the to-be-ignored stimulus, as this was irrelevant throughout the experiment. In the two experiments reported here, cues similar to those studied in saccade tasks are examined with selective reaching procedures. Experiment 1 shows that when a coloured light-emitting diode cue, upon which subjects engage and then subsequently disengage attention, is close to the responding hand, the hand deviates away from the cue. Experiment 2 confirms this cue avoidance by showing that, compared with central fixation alone, the hand veers away from a central cue. These results confirm that the path deviations observed in saccades can also be obtained in manual reaching movements. Such findings support the notion that eye and hand movements are both affected by inhibitory mechanisms of attention.

Acoustic Stimulation↗

PubMed1997

Object-based facilitation and inhibition from visual orienting in the human split-brain.

Object-based attention was examined in 2 split-brain patients. A precued object could move within a visual field or cross the midline to the opposite field. Normal individuals show an inhibition in detecting signals in the cued object whether it moves within or between fields. Both patients showed this effect when the cued object moved within a visual field. When it crossed the midline into the opposite visual field, however, detection was faster in the cued box. These results reveal both facilitatory and inhibitory effects on attention that are object based and may last for several hundred milliseconds. However, the inhibition requires an intact corpus callosum for interhemispheric transfer, whereas the facilitation is transferred subcortically.

Adult↗

PubMed1997

Externally cued and internally generated selection: differences in distractor analysis and inhibition.

In most studies of selective attention, the experimenter informs the participant what the target is and what action is required. For example, participants may be told to name the red drawing. The present study shows that under such conditions of external selection, distractor inhibition is used to ensure that selection is efficient. In external selection, analysis of distractors is limited, causing later recognition of distractor items to be poor. In contrast, during real-world selection a person may be confronted with a number of potential targets and may have to decide what will be the target for action. Under these conditions of internal selection, inhibition of distracting information does not occur. Moreover, distractors are more fully analyzed and thus better recognized at a later test.

Analysis of Variance↗

PubMed1996

Inhibitory mechanisms of neural and cognitive control: applications to selective attention and sequential action.

This paper discusses the role of inhibition in neural and cognitive control, in particular its role in selective processes in perception and action. We first review neuroanatomical and physiological evidence that cortical control is mediated by a variety of local-circuit inhibitory neurons, distributed throughout all layers and areas of the cortex. We then consider the use of inhibition in control processes in behavioral neural network models, focusing on two areas: selective attention and sequential action. Relations between the architecture and dynamics of these models and relevant neurological findings are discussed. We conclude that a full understanding of inhibitory control of mental functioning will require the integration of data from both the behavioral and neural levels, and that formal neural network models can play an important role in bridging this epistemological divide.

Attention↗

PubMed1996

Representational momentum and memory for luminance.

Representational momentum (RM) is a distortion in memory for the final position of an object in the direction implied by a set of discrete inducing displays (J.J. Freyd, 1987; J.J. Freyd & R.A. Finke, 1984). The effect has been shown under a wide variety of circumstances, which has led to assertions that it is a general enough phenomenon to extend to virtually any dimension of change. It is reported here that decisions about luminance seem not to be subject to RM. Instead, a robust effect in the direction opposite to that predicted by the RM hypothesis was observed. It is argued that RM might be more usefully considered limited to dimensions of change correlated with motion in the real world, and some initial hypotheses as to the nature of the mechanism underlying this new luminance effect are presented.

Adult↗

PubMed1996

Object-centered not scene-based visual neglect.

Whether visuospatial attention accesses object-centered representations, in addition to location-based coordinates, was investigated in patients with hemispatial neglect who detected a target on the left or right of a single object (2 connected circles or barbell) or of 2 objects (2 unconnected circles). The object or objects either remained static (left circle in left space) or rotated by 180 degrees (left circle now in right space). Relative to the static condition, in the rotating condition, detection times are facilitated on the left (contralateral) and inhibited on the right (ipsilateral) of space even when eye movements are controlled. This modulation of neglect was only observed for the single object, but not for the 2-object displays. The findings suggest that attention operates on object-centered as well as on location-based representations, and thus accesses multiple reference frames.

Aged↗

PubMed1996

Inhibition of return to successively cued spatial locations: commentary on Pratt and Abrams (1995).

J. Pratt and R.A. Abrams (1995) reported that the inhibition of return of attention is found only for the most recently attended of 2 cued locations. This study does not dispute their findings, but suggests that a more ecologically valid experiment would have more than 2 possible target locations. Twelve male students participated in an experiment in which the target may occur in 1 of 4 possible locations, after 3 of those locations have been cued exogenously in sequence. Inhibition of return was found for each of the cued locations. This result suggests that inhibition may be an important mechanism for aiding visual search in complex environments.

Adult↗

PubMed1994

Object-based and environment-based inhibition of return of visual attention.

Efficient search for an object often requires that attention be prevented from returning to recently examined environmental loci. M. I. Posner and Y. A. Cohen (1984) proposed that inhibition of return (IOR) of visual attention is a search mechanism that prevents such attentional perservation. The internal representations upon which IOR functions were examined and the following conclusions were drawn: First, IOR mechanisms have access to both object- and environment-based representations. Second, environment-based inhibition can be associated with a featureless environmental location, whereas the object-based mechanism requires that attention be oriented to a visible object. These findings are discussed in terms of physiological pathways that may mediate location- and object-based effects.

Attention↗

PubMed1992

Selective reaching: evidence for action-centered attention.

Most studies of selective attention briefly present static 2-dimensional stimuli and require arbitrary responses such as verbal naming or a keypress. Many of our perceptual-motor interactions with the environment, however, require reaching directly toward an object while ignoring other objects in the scene. A series of experiments examines selective attention in the latter reaching situation. Effects previously observed in the traditional experimental procedures were obtained, suggesting that the models developed (which propose inhibitory mechanisms, e.g.) apply to ecologically valid situations. Attention accesses action-centered internal representations during such tasks.

Adult↗