Biomedical subjects

J Laarni

Publications and source records attributed to J Laarni.

5 recordsLinked to original sources

PubMed1999

Cues facilitate detection of motion in dynamic random-dot patterns.

In 1981 Ball and Sekuler showed that a briefly flashed line which primed the subject to the direction of target motion improved the detection of a target. Our aim was to study whether a pointing arrow and random-dot patterns that move in one of four possible directions can prime detection of motion for higher-contrast stimuli. When the motion of a target was primed and the cue validity was 100%, the target's position was more easily detected. Improvement was significant when the direction indicated by the cue and a target's direction were either the same or opposite relative to each other. When the subjects (n = 5 each experiment) did not know the direction of the target before the presentation of the stimulus field, no improvement was found. A discussion of attention to the cue is presented.

Adult↗

PubMed1997

Shape priming in a complex visual search task.

Shape priming was studied in four experiments comprising a complex search task in which subjects searched for a target shape presented among three distractors and reported the location of the target. Localization performance improved as a function of the duration of stimulus exposure and prime lead time. The efficiency of shape primes in improving performance decreased when lateral masks were presented near the target. Generally, both preprimes and simultaneous primes improved localization accuracy. With laterally masked stimuli, the preprimes and simultaneous primes were equally effective; when neighboring mask items were absent, the effect of preprimes was more pronounced. The results suggest that different strategies were used in the preprime and in the simultaneous-prime conditions.

Cues↗

PubMed1996

Foveal-to-peripheral priming in letter identification reflects response bias, not enhanced visibility.

Several studies have suggested that it might be easier to identify a letter when its replication is simultaneously presented in the visual display. We have measured identification accuracy for a memorized target letter that was shown in the peripheral field in two conditions in which a letter either identical or different in shape was flashed simultaneously at fixation. The results of three forced-choice experiments showed that, contrary to Geiger and Lettvin's (1986) previous findings, an identity prime did not improve the visibility of a temporally backward masked target letter. However, the foveal prime letter could apparently bias the subject's decision so that he/she was much more ready to report the more visible prime letter as the peripheral target.

Adult↗

PubMed1996

Performance in simple visual search at threshold contrasts.

PURPOSE: Visual search for a target, orthogonal to distractors (nontargets) in orientation, has been shown to be independent of the number of distractors (set size). This finding has been thought to indicate that the search occurs spatially in parallel and without capacity limitations. The current study was designed to test whether an orientation difference of 90 degrees between the target and distractor gratings would produce a set-size effect when performance was measured at contrast threshold, that is, whether the threshold contrast at which the target was detected among distractors increased as a function of the number of distractors. The second question studied was whether signal-position uncertainty could explain the possible set-size effect. METHODS: The observer searched for a horizontal Gabor patch target in a two-interval, forced-choice task. In the search condition, the target patch was among seven vertical distractor Gabors, all positioned along an isoeccentric circle. The number of possible display locations monitored by the observer varied, and, before each block, he was informed which locations were relevant. In the single-element condition, the target appeared alone, but the number of possible target locations varied as above. RESULTS: In both conditions, the contrast thresholds almost doubled when the number of possible target locations increased from 1 to 8. CONCLUSIONS: Even though the orientation difference between target and distractors was maximal, a set-size effect was found. The effect could be explained by positional uncertainty.

Contrast Sensitivity↗

PubMed1994

Temporal properties of colour and shape priming: evidence of multiple components of attention.

It has been shown in several studies that the selection of letters or numerals from an array can occur efficiently if criteria such as location, colour, shape, or size are used. It is also known that there are at least two components of spatial attention, the transient exogenous and the sustained endogenous. An interesting question is whether it is possible to elicit similar components when colour or shape information is used as a selection criterion. Experiments are reported the aim of which was to try to produce colour or shape precue effects on location and colour/shape discrimination accuracy, and to determine the minimum latency of these effects by sampling numerous cue lead times from 0 ms to 1000 ms. The results showed that, although accuracy did not increase monotonically with increased cue lead time, there were two transient peaks of performance at cue lead times of 0-200 ms, culminating at 30-50 ms and at 160-200 ms. It is suggested that the first component reflects nonspecific exogenous activation, triggered by the onset of a cue; the second component, in turn, may reflect feature-specific endogenous activation related to selection by colour or shape.

Attention↗