Arrangement Of Stimuli Research Articles

Attentional Bias toward Low-Intensity Stimuli: An Explanation for the Intensity Dissociation between Reaction Time and Temporal Order Judgment?

If two stimuli need different times to be processed, this difference should in principle be reflected both by response times (RT) and by judgments of their temporal order (TOJ). However, several dissociations have been reported between RT and TOJ, e.g., RT is more affected than TOJ when stimulus intensity decreases. One account for these dissociations is to assume differences in the allocation of attention induced by the two tasks. To test this hypothesis, different distributions of attention were induced in the present study between two stimulus positions (above and below fixation). Only bright stimuli appeared in one position and either bright or dim stimuli in the other. In the two RT experiments, participants had to respond to every stimulus appearing in one of the two positions. Reaction times to bright stimuli were faster when they appeared in the position where dim stimuli were likely to occur. This finding suggests that the allocation of attention was adapted to the asymmetrical arrangement of stimuli, not suggested by explicit instruction. In the two TOJ experiments, the temporal order of stimuli appearing in the two positions had to be judged. Although bright stimuli appearing at the bright-and-dim location were judged to be earlier, this effect was small and insignificant. Further, the intensity dissociation between RT and TOJ was insensitive to random vs blockwise presentations of intensities, therefore was not modified by attentional preferences. Thus, asymmetrical arrangement of stimuli has an impact on the allocation of attention, but only in the RT task. Therefore dissociations between TOJ and response times cannot be accounted for by an attentional bias in the TOJ task but probably by different use of temporal information in the two tasks.

Perceptual organization of apparent motion in the Ternus display.

A typical Ternus display has three sequentially presented frames, in which frame 1 consists of three motion tokens, frame 2 (blank) defines the interstimulus interval, and frame 3 has similar motion tokens with their relative positions shifted to the right. Interestingly, what appears to be a seemingly simple arrangement of stimuli can induce one of two distinct apparent-motion percepts in the observer. The first is an element-motion perception where the left-end token is seen to jump over its two neighboring tokens (inner tokens) to the right end of the display. The second is a group-motion perception where the entire display of the three tokens is seen to move to the right. How does the visual system choose between these two apparent-motion perceptions? It is hypothesized that the choice of motion perception is determined in part by the perceptual organization of the motion tokens. Specifically, a group-motion perception is experienced when a strong grouping tendency exists among the motion tokens belonging to the same frame. Conversely, an element-motion perception is experienced when a strong grouping tendency exists between the inner motion tokens in frames 1 and 3 (i.e. the two tokens that overlap in space between frames). We tested this hypothesis by varying the perceptual organization of the motion tokens. Both spatial (form similarity, 3-D proximity, common surface/common region, and occlusion) and temporal (motion priming) factors of perceptual organization were tested. We found that the apparent-motion perception of the Ternus display can be predictably affected, in a manner consistent with the perceptual organization hypothesis.

Angioscotoma detection with fundus-oriented perimetry. A study with dark and bright stimuli of different sizes.

Fundus-oriented perimetry (FOP) was used to evaluate the effectiveness of different-sized bright and dark stimuli in detecting and quantitatively measuring angioscotoma. The foveolas and optic disks of digitized fundus images were aligned with their psychophysical counterparts to construct individual grids of perimetric stimuli. Each grid included a linear set of test point locations crossing a retinal vessel. Angioscotomas immediately became visible in nine of 13 healthy normal volunteers tested with FOP. Additional mathematical processing of local loss of differential light sensitivity (dls) disclosed an angioscotoma for at least one stimulus condition in all persons tested. The angioscomas were usually deeper for small (12) targets than for large (32') ones. On the other hand, the overall noise at dls thresholds was generally higher for small than for large stimuli regardless of whether the stimuli were bright or dark. No noteworthy differences were found in detection rates or signal-to-noise ratios under different stimulus conditions (dark/bright/small/large). FOP permits the individual arrangement of stimuli for specific morphological conditions and is thus capable of detecting even minute visual field defects such as angioscotomas.

The Effects of Response Effort and Choice on Productivity

The purpose of this study was to examine the effects of response effort, novelty of stimulus arrangement, and choice on selecting behavior of an individual with profound mental retardation in a vocational setting. Data showed that: (a) novelty of stimulus array, not response effort, affected selecting behavior, and (b) choice affects behavior only to the extent that preferred outcomes are attained. Results are discussed in relation to matching theory.

Cross-language tests of hemispheric strategies in reading nonwords.

Four experiments explored the effects of specific language characteristics on hemispheric functioning in reading nonwords using a lateralized trigram identification task. Previous research using nonsense consonant-vowel-consonant (CVC) trigrams has shown that total error scores reveal a right visual field (RVF) advantage in Hebrew, Japanese, and English. Qualitative error patterns have shown that the right hemisphere uses a sequential strategy, whereas the left hemisphere uses a more parallel strategy in English but shows the opposite pattern in Hebrew. Experiment 1 tested whether this is due to the test language or to the native language of the participants. Results showed that native language had a stronger effect on hemispheric strategies than test language. Experiment 2 showed that latency to target letters in the CVCs revealed the same asymmetry as qualitative errors for Hebrew speakers but not for English speakers and that exposure duration of the stimuli affected misses differentially according to letter position. Experiment 3 used number trigrams to equate reading conventions in the 2 languages. Qualitative error scores still revealed opposing asymmetry patterns. Experiments 1-3 used vertical presentations. Experiment 4 used horizontal presentation, which eliminated sequential processing in both hemispheres in Hebrew speakers, whereas English speakers still showed sequential processing in both hemispheres. Comparison of the 2 presentations suggests that stimulus arrangement affected qualitative errors in the left visual field but not the RVF for English speakers and in both visual fields for Hebrew speakers. It is suggested that these differences result from orthographic and morphological differences between the languages: Reading Hebrew requires attention to be deployed to all the constituents of the stimulus in parallel, whereas reading English allows sequential processing of the letters in both hemispheres. Implications of cross-language studies for models of hemispheric function are discussed.

CS modality transfer of two-way avoidance in rats with central and basolateral amygdala lesions

Post-lesion acquisition of two-way avoidance and subsequent transfer to two warning signals (conditioned stimulus, CS) of different modality were investigated in 60 rats. In Experiment I the animals were originally trained with less salient (darkness) CS, then transferred to more salient compound (darkness and white noise), and finally to white noise CS. The opposite arrangement of the conditioned stimuli (CSi) during the subsequent stages was employed in Experiment II. In control animals, avoidance acquisition was faster and the intertrial responding (ITR) rate lower with the auditory than with the visual CS. Lesioned rats learned avoidance responses more slowly, independently of CS modality. The transfer to other CSi revealed dramatic between-group difference in the level and consistency of avoidance response, shuttle-box latencies and ITR rate. In control animals, transfer to more salient CSi enhanced avoidance performance, whereas change to less salient CS decreased it. Rather small changes in shuttle-box performance and consistency of avoidance response due to CS modality were seen in rats with the basolateral lesions. In contrast, central nucleus injury caused a strong deterioration in the avoidance transfer, especially when the visual CS followed the acoustic one. The results indicate differential involvement of the basolateral and central amygdala nuclei in stimulus-processing mechanisms of instrumental defensive behavior.

A RESPONSE‐RESTRICTION ANALYSIS OF STEREOTYPY IN ADOLESCENTS WITH MENTAL RETARDATION: IMPLICATIONS FOR APPLIED BEHAVIOR ANALYSIS

The behavior of 4 adolescents with severe or profound mental retardation was evaluated in the presence of four sets of materials during periods of unstructured leisure activity. Functional engagement with the materials, stereotypic engagement with the materials, stereotypy without interaction with the materials, and other aberrant behaviors were recorded. Across a series of experimental conditions, the number of sets of materials was reduced from four to one by eliminating the set most frequently manipulated in each preceeding condition. In the final condition, four sets of materials were again made available for manipulation. The procedures replicated Green and Striefel's (1988) response-restriction analysis of the activity preferences and play behaviors of children with autism. In general, the results of the present experiment replicate those of Green and Striefel in that reallocation of responding was idiosyncratic and unpredictable as sets of materials were removed. Nevertheless, the results provided insight into how responding might be reallocated if it were restricted through behavioral interventions rather than by restriction of access. Thus, the results are discussed with respect to how response-restriction analyses may be useful in identifying topographies of behavior that could be included in differential reinforcement contigencies that are designed to affect stereotypic behavior and in the selection and arrangement of environmental stimuli to minimize the presence of evokers of stereotypy.

Primitives Used in the Spatial Localization of Nonabutting Stimuli: Peaks or Centroids

In order to determine whether simple luminance profiles are located by their peaks or centroids we performed a three element alignment task where the central element's degree of luminance asymmetry was randomly chosen from a flat distribution (skew noise). The central element with its randomly chosen skew was either positioned using the peak or centroid of its distribution. Accuracy is invariant with the magnitude of the skew noise for the centroid but not the peak condition. We conclude that the human visual system assigns position tags using centroids not peaks of luminance distributions for gabors. However this is not the case for Gaussian blobs, where a measure closer to the midpoint is used for our stimulus arrangement. Copyright © 1996 Published by Elsevier Science Ltd.

Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams.

Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams.

Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams.

Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams.

Associative learning: Stimulus arrangement and response consistency

AbstractStudies on associative learning in normals and patients need appropriate dependent measures which are sensitive enough to reflect stimulus-specific responses and also consider the context in which the conditioning takes place. Patient's fear responses, once acquired, seem to be maintained by specific cognitive biases such as individual belief systems and a tendency to stay consistent with their previous judgments.

The relation of lightness and stereoscopic depth in a simple viewing situation

The effect of stereoscopic depth on perceived lightness was studied using a simple, achromatic stimulus arrangement. In Experiment 1, depth/lightness interactions were sought between a single test field and a single induction field. In Experiment 2, depth/lightness interactions were looked for between a single test field and two induction fields. Stimuli were presented on a computer screen and viewed with a stereoscope. The subjects reported perceived lightness of the achromatic test field by rating its apparent blackness along a dimension of 0%-100%. In Experiment 1, they reported lightness judgments of the test field across 13 perceived depth levels and 8 contrast levels. In Experiment 2, they gave lightness judgments of the test field across 7 perceived depth levels and 16 contrast levels. We were particularly interested in observing the generality of Gilchrist's coplanar ratio hypothesis. The results showed that when stereopsis and contrast levels are the available cues, depth and lightness percepts are independent, and it is retinal ratios, not coplanar ratios, that dictate lightness perception. We conclude that before the relative depth location of an object is determined, its lightness value is known through sensory-level processes.

Manipulating the spatial arrangement of stimuli in a precuing task

Within the context of the spatial precuing paradigm a consistent finding is that, with hands placed adjacently, precuing of two fingers on the same hand results in faster discrete finger responses than precuing of two fingers on different hands. This phenomenon is known as the ‘hand advantage’. The present study examined the possibility that perceptual factors contribute to this hand advantage. Results showed that the perceptual manipulation of moving the two center stimulus positions each one position inwards significantly reduced the hand advantage over the first 250 ms of preparation interval. This result was interpreted as reflecting a perceptual locus of the hand advantage. Perceptual encoding processes were tentatively postulated to operate according to the familiar subgroup hypothesis, which claims that spatial precues may differ in the ‘familiarity’ or ‘strength’ of the subgroups they create. The fact that a significant hand advantage remained present was taken as evidence in support of post-perceptual processes mediating the hand advantage. On the basis of these findings we argue that both perceptual and post-perceptual processes play a role in the spatial precuing task and mediate the hand advantage.

The multimeridional apparent frontoparallel plane: introduction of the induced effect.

The application of vertical rod stimuli to obtain apparent frontoparallel plane (AFPP) settings is well-known. A geometrical relation based on observation distance, interpupillary distance, and retinal disparity determines the deviation of the setting from the objective frontoparallel plane. Further developments of this procedure have established that a similar relation exists for oblique presentations of parallel rod stimuli, the orientation of the rods being an additional variable. This extension of the AFPP procedure is referred to as the multimeridional AFPP or MAFPP. It permits the determination of aniseikonia in oblique as well as horizontal meridians. Although oblique disparities contain a vertical component, an induced effect is absent as long as parallel rod stimuli are used alone. If an induced effect were present, the MAFPP geometrical relations would be expected to break down. To test this hypothesis, random dot arrays and a row of dots of the same frequency as a control stimulus of parallel lines were presented alone and in combination with the line stimuli. Binocular disparities were induced by a meridional afocal magnifier placed at various axes before one eye. It was found that the dot arrays caused a breakdown of the geometrical relation when presented alone or in combination with the parallel lines. The amount of deterioration varied only slightly with the number and arrangement of dot stimuli but increased as the vertical component of the oblique magnification increased. In addition to proving the main hypothesis, the data provide information pertaining to the MAFPP theory as well as offering some insight into the induced effect. The most important practical implication of the results is that the MAFPP theory can be used to measure unknown retinal disparities only if continuous parallel lines are presented in isolation.

Motor coactivation revealed by response force in divided and focused attention.

Four experiments examined effects of bimodal stimulation on response force (RF) in addition to reaction time (RT). In a divided-attention task (Experiments 1 to 3), subjects were asked for a speeded response to either a visual or an auditory signal. In unimodal signal trials, either a visual or an auditory signal was presented alone, and in redundant-signals trials, both signals were presented simultaneously. The same stimulus arrangement was used in a focused-attention task (Experiment 4), but subjects had to withhold their response when an auditory signal was presented alone. In all experiments, the fastest RTs were attained in redundant-signals trials. In addition, RF was largest in redundant-signals trials, especially in the divided-attention task, suggesting a motor coactivation hypothesis. The results indicate that the type of stimulation influences not only when a response is initiated but also how the response is executed. This finding challenges the view, commonly held in mental chronometry, that late motoric processes remain untouched by experimental manipulations. A detailed analysis of the relationship between RT and RF revealed that these variables are not inherently redundant measures, and, therefore, RF recording may supplement the traditional RT measurement in mental chronometry.

A “popout” effect with words and nonwords

Previous research (Flowers & Lohr, 1985) has not found evidence for the “popout” phenomenon (e.g., Treisman, 1988) with word and nonword letter strings. Flowers and Lohr utilized a visual search task that employed a circular arrangement of stimuli. This format does not optimize spatial contiguity, which has been shown to facilitate stimulus detection in certain contexts (Bryant & Soraci, 1992; Soraci, Carlin, Deckner, & Baumeister, 1990). The present study examined popout with words and nonwords in a same-different task, using a visual array format in which interstimulus contiguity increased with changes in set size. With these arrays, no popout effect was evidenced under conditions of high featural overlap between targets and distractors. However, under conditions of low featural overlap, a popout effect for both words and nonwords was found.

Spatial and configural factors in compound stimulus processing by pigeons

Three matching-to-sample experiments examined whether spatial or configural factors determined how the element arrangement of compound sample stimuli influenced matching accuracy in pigeons. Seven types of compound stimuli were tested. The arrangement of color and line-orientation elements in these compounds varied in terms of the spatial separation between the elements, the degree of consistency in element spatial location, and the number of bounded areas containing the elements. Matching accuracy was examined upon initial exposure to the compounds, during asymptotic conditions of shared attention, and with variation of sample durations ranging from .04 to 5.935 sec. In all three experiments, when spatial proximity, locational certainty, and the number of lines were precisely controlled or equated, no evidence for the proposed configural processing of “unified” compounds was found (Lamb & Riley, 1981). Element spatial separation, and to a lesser degree perceptual limitations, determined compound performance. These results question our lab’s previous evidence for configural compound processing by pigeons (Lamb, 1988; Lamb & Riley, 1981). They suggest instead that pigeons independently and separately process the individual elements of color/line-orientation compounds, with element separation determining the distribution of processing between the elements.

Electrical responses to short-range kinematogram displays: an occipital lobe global motion process in humans?

In a series of studies Manning et al. have investigated visual evoked potentials (VEPs) in response to different “classes” of apparent motion (AM) displays; shortrange (random-dot kinematograms, Manning, Finlay 8z Fulham, 1991), long-range (simple two-element displays, Manning, Finlay & Fenelon, 1988; Manning 8z Finlay, 1989a; Finlay & Manning, 1991), and rotary (the “waggon-wheel effect”, Manning & Finlay, 1989b). Short-range AM was investigated using dynamic kinematogram displays very similar to those used by Braddick (1974). VEPs were recorded in a number of experimental conditions in which the magnitude of the lateral displacement of a central rectangular region was varied (Manning et al., 1991). A number of VEP components were identified, and each of these was focussed over midline occipital cortex. For one of the components, amplitudes were significantly lower in response to lateral displacements within the limits of “short-range AM” than in response to lateral displacements beyond the limits (beyond D,,). In addition to recording VEPs from kinematograms in which the subjective percept of motion was manipulated by varying the magnitude of displacement, Manning ef al. (1991) also made use of the bistable nature of AM effects to record VEPs associated with different perceptual states. For most AM displays, an identical set of stimulus parameters may produce either the strong impression of a single object in motion, or alternatively may fail to produce such a percept. In the case of random dot kinematograms an identical stimulus arrangement may produce either the impression of a single moving object (the rectangular displacement region of dots), or may produce the impression of incoherent movement of individual stimulus elements in all directions within the displacement region. The loss in identity of the single object in motion (for long-range AM) has been termed the “AM breakdown effect” (Finlay & von Griinau, 1987). Using this breakdown effect Manning et al. (1991) presented a single subject with a random dot kinematogram display and recorded VEPs from a single

Orientation acuity estimated with simultaneous and successive procedures.

Orientation discrimination thresholds for medium contrast sinewave grating stimuli were estimated by a forced-choice procedure for the two principal, and the two main oblique axes. The results obtained for simultaneous presentation with a centre/surround stimulus arrangement are compared with the threshold estimates obtained when the two stimuli to be discriminated do not overlap in time. We find that orientation acuity depends on the temporal relationship of the discriminanda. Estimates of orientation threshold with simultaneous presentation are lower on all axes tested than those obtained with successive presentation; the greatest difference in orientation acuity was found at obliques. The data support the hypothesis that the meridional anisotropy in orientation discrimination that is found with conventional, two-interval forced-choice methods is not entirely attributable to anatomical and physiological changes at the level of the striate cortex.

Role of the preprobe delay in memory-scanning tasks

In a variation of Sternberg's (1966, 1969) memory-scanning task not requiring an explicit negative response, Diener (1988) found that a preprobe delay was necessary to produce the usual set-size effect. In Experiment 1 of the present study, the effect of the preprobe delay was investigated in the typical two-response task. In the absence of a preprobe delay, the function relating response latency to set size was virtually flat for negative responses, but was described by a slope of about 18 msec/item for positive responses. Further research suggested that the reduced set-size effect in the absence of a preprobe delay is the result of expectancy effects usually controlled by the preprobe delay. Informing the subject of the size of the memory set before it was presented (Experiment 2) produced a set-size effect of the usual magnitude in the absence of a preprobe delay. Experiment 3 was designed to assess the effects of expectancy in the absence of a memory search. A task similar in stimulus arrangement to the memory-scanning task but requiring the subject to indicate whether the last digit in the set was odd or even produced a decrease in response latency with set size of 29 msec/item in the absence of a preprobe delay.