Biomedical subjects

P J Keuss

Publications and source records attributed to P J Keuss.

18 recordsLinked to original sources

PubMed2001

Focused attention reduces the effect of lateral interference in multi-element arrays.

Lateral interference of nearby irrelevant flankers may be reduced when attention is already focused at a relevant position. This hypothesis was tested in three experiments with multi-element arrays consisting of one target and several neutral flankers with reaction time (RT) and proportion of errors (PE) as dependent variables. The arrays were preceded by peripheral cues that varied in size to induce different levels of focused attention. In a first experiment, the eccentricity effect was shown to be affected by attention, but no support was found for a reduction of lateral interference in the case of focused attention. However, these results may be due to an attentional bias for central elements. Two additional experiments were performed in which target-flanker distance was manipulated. RTs and PEs showed that the effect of target-flanker distance was smaller when the precise target position was indicated by a peripheral precue. Thus, focused attention seems to reduce the effect of lateral interference. These results can be explained most easily by a model in which attention already affects early perceptual processing.

Adult↗

PubMed1996

Threefold effect of peripheral precues: alertness, orienting, and response tendencies.

Three experiments were run revealing that peripheral cues exert an alerting and orienting effect. Novel is the finding that peripheral cues induce a (hidden) tendency to respond to the cued side, which interacts with the response tendency elicited by the subsequent following target. Compatible S-R mappings revealed either a reversed or no response tendency in cue conditions as compared to uncued conditions. Incompatible mappings mostly showed a decrease in response tendencies under influence of the peripheral cue. An increase of the interval between the cue and the target up to 500 ms resulted in a return to the baseline condition (without cue). The findings for the compatible mappings may be interpreted in terms of an extra recoding operation that was induced by peripheral cues. Inconsistencies found for incompatible S-R mappings might be attributed to the dual presence of recoding operations on account of the cue and the target.

Adult↗

PubMed1993

Does the production of letter strokes in handwriting benefit from vision?

In earlier studies the involvement of vision in handwriting was suggested by the finding that the production of a letter sequence in a condition without vision took more time and resulted in larger letter trajectories. The present study raises the question whether vision has an impact on the production of the individual up- and downstrokes constituting the letters. More specifically, the aim is to examine whether vision is employed either during the completion of a movement, or concurrent with the entire course of a stroke movement. Adult writers produced the letter sequence lelele under a no-vision and a vision condition, the latter serving as a base-line condition. It was found that movement time and trajectory size of acceleration and deceleration phases of a stroke movement increased under no vision, the magnitude of which depended on letter type. Letter e, with a smaller size and more frequently used in Dutch writing than letter l, was less affected by the no-vision condition. Although, close examination of downstrokes produced in later letter positions of the sequence revealed that the acceleration as compared to the deceleration phase took proportionally less time, the general finding was that increments in time and size proved to be equally distributed across entire stroke movements.

Adult↗

PubMed1992

The role of vision in the temporal and spatial control of handwriting.

The general observation that handwriting is not noticeably impaired by the withdrawal of vision can be explained in two ways. One might argue that vision is not needed during the act of writing. Micro-analyses should then reveal that spatial as well as temporal writing features are identical in conditions of vision and no vision. Alternatively, it is possible that vision is needed during the act of writing, but that without vision possible errors and inaccuracies have to be prevented. Assuming that the latter would place an extra demand on movement control, this should be revealed by an increase in processing time. We have found evidence for the latter view in the present study in which 12 subjects wrote a nonsense letter sequence with and without vision. Close examination showed that writing shapes remained equally invariant under both vision conditions, suggesting that spatial control was unaffected by withdrawing vision. The prediction that invariance of shapes is preserved in the absence of vision at the expense of processing time increments was confirmed. The increase of reaction time observed when visual guidance was withdrawn suggests that more processing time was needed prior to the movement start. Moreover, the RT increment was larger when a short writing duration was instructed. The present findings will be discussed in light of the remarkable flexibility of writing as a motor skill in which writers appear to be able to employ specific strategies to preserve shape in the absence of visual guidance.

Adult↗

PubMed1990

Auditory accessory effects on visual processing.

A series of experiments on intersensory facilitation demonstrates that non-informative sound of low to moderate intensity (30/80 dB) facilitates the reaction to a visual stimulus. By manipulating the preprocessing and perceptual stages of the visual signals, it appears that auditory intensity reduces choice reaction time independently from the positive influence of the intensity and duration of the visual imperative signal, but interacts with the effect of stimulus degradation. Degraded stimuli take more profit of the sound than intact stimuli. Besides a short-term activation effect, originated by accessories of the auditory modality, on the motor adjustment stage (cf. Sanders 1983), the results suggest that the accessory influences the stage of feature extraction.

Adult↗

PubMed1989

An additive factors analysis of the effect(s) of location cues associated with auditory stimuli on stages of information processing.

The additive factors method (AFM) was used as a tool for assessing the locus (or loci) of the detrimental effect of auditory location cues in the chain of (visual) information processing. In the first experiment the location variable was factorially combined with response specificity, which is assumed to affect the response adjustment stage. A second experiment was performed in which movement amplitude, assumed to affect the response programming stage, was manipulated in addition to the location variable and a different variety of response specificity. Finally, the location variable was combined with relative S-R frequency, which is also assumed to affect the response programming stage, in a third experiment. The results of these experiments showed additive effects of the location variable with motor variables. The remaining two experiments were designed to assess the effects of location cues on response selection. In these experiments the location variable was combined with the number of response alternatives. Response speed decreased with an increase in the number of response alternatives. However, the effects of the location variable and number of response alternatives were additive. According to the additive factor logic, then, the results of experiments 1, 2 and 3 seem to indicate that the locus of interference of the location cues is not in the later response stages of the reaction process. The results of the last two experiments were interpreted to suggest that the effects of location cues and the number of response alternatives affect either different processes within the response selection stage or affect different process stages. It was concluded that the latter alternative explains most of the data currently available and that the stimulus identification stage is the most likely candidate for the locus of the location effect.

Adolescent↗

PubMed1986