Biomedical subjects

E Poliakoff

Publications and source records attributed to E Poliakoff.

9 recordsLinked to original sources

PubMed2005

Visuotactile temporal order judgments in ageing.

We report an experiment on the effects of ageing on crossmodal temporal perception. Young (mean age = 21.7 years) and old (mean age = 75.1 years) participants were presented with pairs of visual and vibrotactile stimuli to either hand and required to make unspeeded temporal order judgments (TOJs) regarding which sensory modality appeared to have been presented first. The stimulus onset asynchrony (SOA) between the two stimuli was varied using the method of constant stimuli. Temporal precision, as indexed by the just noticeable difference (JND), was better (i.e., JNDs were lower) when the stimuli were presented from different positions (M = 101 ms) rather than from the same position (M = 120 ms), as has been demonstrated previously. Additionally, older observers required more time (i.e., their JNDs were larger) to accurately perceive the temporal order (M = 131 ms) as compared to younger observers (M = 98 ms). Our results confirm that ageing deleteriously affects crossmodal temporal processing even when the spatial confound inherent in previous research has been ruled out.

Adult↗

PubMed2005

Paying attention to saccadic intrusions.

Fixation to a target in primary gaze is invariably interrupted by physiological conjugate saccadic intrusions (SI). These small idiosyncratic eye movements (usually <1 degrees in amplitude) take the form of an initial horizontal fast eye movement away from the desired eye position, followed after a variable duration by a return saccade or drift. As the aetiology of SI is still unclear, it was the aim of this study to investigate whether SI are related to exogenous or endogenous attentional processes. This was achieved by varying (a) the "bottom-up" target viewing conditions (target presence, servo control of the target, target background, target size) and (b) the 'top-down' attentional state (instruction change--'look' or 'hold eyes steady' and passive fixation versus active--'respond to change' fixation) in 13 subjects (the number of participants in each task varied between 7 and 11). We also manipulated the orientation of pure exogenous attention through a cue-target task, during which subjects were required to respond to a target, preceded by a non-informative cue by either pressing a button or making a saccade towards the target. SI amplitude, duration, frequency and direction were measured. SI amplitude was found to be significantly higher when the target was absent and SI frequency significantly lower during open loop conditions. Target size and background influenced SI behaviour in an idiosyncratic manner, although there was a trend for subjects to exhibit lower SI frequencies and amplitudes when a patterned background was present and larger SI amplitudes with larger target sizes. SI frequency decreased during the "hold eyes steady" passive command as well as during active fixation but SI direction was not influenced by the exogenous cue-target task. These results suggest that SI are related to endogenous rather than exogenous attention mechanisms. Our experiments lead us to propose that SI represent shifts in endogenous attention that reflect a baseline attention state present during laboratory fixation tasks and may prove to be a useful tool to explore higher cortical control of fixation.

Adult↗

PubMed2005

Attention and selection for predictive smooth pursuit eye movements.

Humans cannot typically produce smooth eye movements in the absence of a moving stimulus. However, they can produce predictive smooth eye movements if they expect a target of a known velocity to reappear. Here, we observed that participants could extract velocity information from two simultaneously presented moving targets in order to produce a subsequent predictive smooth eye movement for one of the two targets. Subjects fixated a stationary cross during the presentation of two targets, moving rightward at different velocities. In the next presentation, a single target was presented, which participants tracked with their eyes. A static cue, presented 700 ms before the moving target, indicated which of the two targets would be presented. Predictive eye movements were of an appropriate velocity, even when participants did not know in advance which of the two targets would subsequently be cued. However, the scaling of predictive eye velocity was marginally less accurate in this divided attention condition than when participants knew the identity of the cued target in advance, or a single target was presented during fixation. In a second experiment, we found that the velocity cued on the previous trial had a greater effect than the uncued velocity on the current trial. The negligible effect of the uncued velocity indicates that participants were extremely effective at selectively reproducing one of two recently viewed velocities. However, other influences, such as past history, also affected predictive smooth eye movements.

Adult↗

PubMed2005

Vision and touch in ageing: crossmodal selective attention and visuotactile spatial interactions.

We investigated whether ageing affects crossmodal selective attention (the ability to focus on a relevant sensory modality and ignore an irrelevant modality) and the spatial constraints on such selective processing. Three groups of 24 participants were tested: Young (19-25 years), Young-Old (65-72 years) and Old-Old (76-92 years). The participants had to judge the elevation of vibrotactile targets (upper/index finger and lower/thumb), presented randomly to either hand while ignoring concurrent visual distractors. In a second task, the role of the target and distractor modalities was reversed. Crossmodal selective attention was assessed by comparing performance in the presence versus absence of distractors. Spatial constraints on selective attention were also investigated by comparing the effect of distractors presented on the same versus opposite side as the target. When attending to touch, the addition of visual distractors had a significantly larger effect on error rates in both of the older groups as compared to the Young group. This indicates that ageing has a detrimental effect on crossmodal selective attention. In all three age groups, performance was impaired when the target and distractor were presented at incongruent as compared to congruent elevations in both tasks. This congruency effect was modulated by the relative spatial location of the target and distractor in certain conditions for the Young and the Young-Old group. That is, participants in the two younger age groups found it harder to attend selectively to targets in one modality, when distractor stimuli came from the same side rather than from the opposite side. However, no significant spatial modulation was found in the Old-Old group. This suggests that ageing may also compromise spatial aspects of crossmodal selective attention.

Adult↗

PubMed2004

Target selection for predictive smooth pursuit eye movements.

Previous work has indicated that after exposure to a moving stimulus, people are able to produce predictive smooth eye movements prior to reappearance of the stimulus. Here, we investigated whether subjects are able to extract relevant velocity information from two simultaneously presented targets and use this information to produce a subsequent predictive response. A trial consisted of a series of two or five presentations of moving stimuli, preceded 500 ms earlier by an audio warning cue. In the first one or four presentations, subjects fixated during the presentation of two moving targets and in the final presentation they tracked a single moving target. During fixation, two moving targets were presented concurrently, originating from the fixation point and moving horizontally to the right at differing velocities (10, 20, 30 or 40 degrees /s), with each target being presented at the same velocity throughout a trial. In the tracking presentation, the fixation cross was extinguished and only a single target was presented, which the subjects were required to track with their eyes. To cue which of the two targets would be presented, the appropriate target was presented statically at the same time as the audio warning cue. A significant relationship was found between eye velocity 100 ms after the start of the tracking target (i.e. prior to visual feedback) and the cued target velocity. Thus, subjects were able to make predictive eye movements that were of appropriate velocity for the cued target, despite fixating and being uncertain which target was relevant, during previous exposure.

Adult↗

PubMed2004

The contribution of non-ocular response inhibition to visual inhibition of return.

Inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. IOR is typically investigated using a cue-target design, in which subjects respond only to the second stimulus of a pair. In such tasks, the measurement of 'true' IOR may be confounded by the effect of non-ocular response inhibition, because the participant must suppress any tendency to respond (e.g. key press) to the first stimulus. This confound may be eliminated using a target-target design, in which responses are made to both stimuli. We assessed the contribution of non-ocular response inhibition to visual IOR, measured in a cue-target task, by testing participants on both cue-target and target-target detection tasks, with identical timings and stimuli. Significant IOR was obtained in both tasks but, at a stimulus onset asynchrony (SOA) of 1400 ms, IOR magnitude was significantly greater in the cue-target condition than in the target-target condition. However, at an SOA of 1800 ms, there was no significant difference in the magnitude of IOR between the two tasks. Thus, a proportion of the total IOR effect observed in visual cue-target tasks can be attributed to non-ocular response inhibition, but this process appears to decay more rapidly than does 'true' IOR, having dissipated by 1800 ms following cue onset.

Adolescent↗

PubMed2002

Tactile inhibition of return: non-ocular response inhibition and mode of response.

Inhibition of return (IOR) refers to the slowing of responses to stimuli presented at the same location as a preceding cue. However, the cue-target paradigm used in most previous studies may have overestimated the contribution of eye movement programming to IOR, due to the existence of manual response inhibition effects. This confound can be circumvented by using a target-target paradigm in which participants respond to all stimuli. Here, we compared IOR magnitude from tactile cue-target and target-target tasks involving identical interstimulus intervals of 1,400 and 1,800 ms. Reaction times were measured using a foot pedal toe-lift response and a vocal response. Tactile IOR was observed using both modes of response, demonstrating IOR for the first time using a non-spatial, vocal response. Moreover, IOR effects were significantly smaller in target-target compared to cue-target conditions, thereby confirming the existence of the response inhibition confound.

Adolescent↗

PubMed2001

Human locognosic acuity on the arm varies with explicit and implicit manipulations of attention: implications for interpreting elevated tactile acuity on an amputation stump.

In Experiment 1, normal subjects' ability to localize tactile stimuli (locognosia) delivered to the upper arm was significantly higher when they were instructed explicitly to direct their attention selectively to that segment than when they were instructed explicitly to distribute their attention across the whole arm. This elevation of acuity was eliminated when subjects' attentional resources were divided by superimposition of an effortful, secondary task during stimulation. In Experiment 2, in the absence of explicit attentional instruction, subjects' locognosic acuity on one of three arm segments was significantly higher when stimulation of that segment was 2.5 times more probable than that of stimulation of the other two segments. We surmise that the attentional mechanisms responsible for such modulations of locognosic acuity in normal subjects may contribute to the elevated sensory acuity observed on the stumps of amputees.

Adolescent↗

PubMed2000

New learning and remote memory in the same and different domains of experience: implications for normal memory and amnesia.

This study investigated the correlation between new and remote memory ability in normal young subjects and evaluated whether using tests that tapped different domains of experience had any effect on the relationship between new and remote memory. Remote memory was assessed using a famous face test and new memory was evaluated using both novel faces and words. The main finding was a significant correlation between New and Remote face familiarity scores. A correlation was obtained when both tests tapped the same domain of memory, whereas when tests tapped different domains, there was no Remote-New correlation. Remote-New correlations may only exist between tests tapping the same domain of memory. This has implications for the interpretation of previous amnesic literature and for future investigations.

Adolescent↗