Effects Of Stimulus Type Research Articles

ERP differences in visual attention processing between attention‐deficit hyperactivity disorder and control boys in the absence of performance differences

Event-related potentials (ERPs) were recorded during a visual two-choice reaction time (RT) task in attention-deficit hyperactivity disorder (ADHD) and control boys selected using strict inclusion and exclusion criteria. No group differences were found in mean RT and correct responses. Although early occipital ERPs were not affected in the ADHD group, the peak latency of early anterior ERPs (N1, P1, N2) was significantly delayed. ADHD showed a larger effect of stimulus type on the frontal negativity (N530) and the posterior late negativity (nSW) and a smaller effect of stimulus type on anterior N2 and posterior P3b amplitude. The development of N530 and P450 amplitude across blocks of five trials was analyzed using orthogonal polynomial trend analysis of variance software. In the control group, P450 amplitude to "frequent" stimuli reduced across blocks. In the ADHD group, N530 amplitude increased for "rare" stimuli across blocks. It is suggested that the ADHD group showed a lack of automatization of the categorization process with increasing time on task for which they compensated by controlled attentional processes.

Asymmetric frontal activation during episodic memory: the effects of stimulus type on encoding and retrieval

Recent functional neuroimaging studies have suggested that the left prefrontal cortex is preferentially involved in the encoding of episodic memory whilst the right prefrontal cortex is preferentially involved in the retrieval of episodic memory, irrespective of the type (e.g. modality) of information being remembered. In the present PET activation study, a 2×2 design was employed to investigate the relationship between encoding and retrieval of verbal and non-verbal material in episodic memory. Accordingly, seven healthy volunteers were scanned whilst encoding and then recalling stimuli which either emphasised visual or verbal processes. When encoding and retrieval tasks were compared directly, significantly greater prefrontal activation was observed in the encoding conditions, regardless of modality, although these changes were bilaterally distributed. In contrast when the verbal and visual memory tasks were compared directly, the former was associated with rCBF changes that were predominantly located in the left lateral frontal cortex whilst the latter was associated with rCBF changes that were predominantly located in the right lateral frontal cortex. These results suggest that encoding and retrieval may actually involve similar regions of the lateral prefrontal cortex when all factors relating to the type of stimulus material (i.e. modality), are appropriately controlled.

Vector analysis of visual evoked potentials elicited by pattern reversal and photic stimuli

Objective: The 2D VEPs to pattern reversal (PR) and LED goggle were studied in order to obtain a stable parameter for the functional assessing of posterior visual pathways regardless of the stimulus type used.Design and methods: Apex c latency, bc segment amplitude (V), and bc vector orientation angle (θ) in voltage space were computed from VEPs recorded in 50 normal human beings and two patients with left posterior brain lesions, in an orthogonal Fpz–Oz and T3–T4 montage and displayed as a two channel Lissajous’ trajectory. The effects of stimulus type and stimulated eye were analyzed in the normal group by a two-way ANOVA.Results: The stimulated eye had no effect on any parameter. Apex c latency was slightly longer, and V was greater and more variable in the responses to goggle stimuli, but there was no significant difference in θ, oriented to mid-occipital scalp with very low variability for both stimulus types. The patients showed significant deviations of θ towards the affected hemisphere.Conclusions: The bc vector orientation (θ) is a stable parameter for the evaluation of the posterior visual pathways using both pattern reversal and LED stimuli, specially the latter, useful in unconscious or uncooperative patients.

The Dynamics of Preschoolers' Categorization Choices

The present research explored the effects of stimulus and task factors on preschoolers' (Experiments 1 and 3) and adults' (Experiment 2) tendency to categorize according to taxonomic relations, when those relations conflict with appearances. In Experiment 1, we examined the effects of and interactions among (a) available information, operationalized by using more- or less-informative stimulus types (objects vs. line drawings) and by the presence or absence of labeling, and (b) task constraints, operationalized by comparing sorting questions with inductive inferences questions. When provided with information that constrained the categorization decision, either through the availability of labels or a combination of enhanced physical informativeness of objects and an inference question, preschoolers reliably based their categorization decisions on taxonomic relations between physically dissimilar items. In Experiment 2, stimulus type (objects vs. line drawings) was shown to have a similar effect on adults. In Experiment 3, we examined the effects of stimulus type on preschoolers' inductive inferences and accuracy of naming. The effects in the two tasks were closely related, suggesting that the amount of available information affects different responses in similar ways. These data demonstrate the interactive effects of available information and task constraints on categorization decisions.

Effects of caffeine on functional asymmetry in a posner letter-recognition task

A Posner task was used to investigate whether caffeine, in common with other drugs, has an asymmetric effect on cerebral functioning. Subjects consumed decaffeinated coffee either with or without added caffeine at 2 mg/kg body weight. They were then required to identify letter-pairs as the same or different. Same was defined as two identical letters irrespective of case (AA, Aa); different was defined as two different letters irrespective of case (AB, Ab). Main effects of stimulus type were found for both accuracy and speed of response. In the noncaffeine condition pattern-matching was faster by the right hemisphere and phonologic matching was faster by the left hemisphere. These results replicate much previous work, but under caffeine, a previously unreported reversal in the balance of hemispheric processing efficiency was found. An explanation is offered in terms of the disruption of the normal, optimum, rate of cerebral processing for each hemisphere.

Detecting simulated amnesia with event-related brain potentials

Two experiments were done in which groups of normal college undergraduate subjects were instructed to simulate autobiographical amnesia related to head injury. The subjects were tested for autobiographical knowledge with pencil-and-paper recall and recognition tasks, and on another day, with recognition tasks in which event-related potentials were recorded in response to the same autobiographical items, this time presented on a display screen. In the first study, three Event-Related Potential (ERP) block types were utilized: 1. 1) a block in which the subject's birthdate was an oddball with p = 0.11 and other dates (not relevant to the subject) had p = 0.89, 2. 2) a block in which phone numbers were used as stimuli, 3. 3) a block in which (mothers' maiden) names were used as stimuli. Only birthdate blocks were used in the second study. A P300 ERP was seen in response to rare, personally relevant items. In both studies, the main effect of stimulus type (personally relevant versus not personally relevant) on P300 amplitude was significant ( p < 0.0001) and there was no main effect of block type in the first study. Under a sophisticated malingering instruction set, about 15% of the items were correctly recalled and about 50% were correctly recognized by simulators in pencil-and-paper tests. Under a naive malingering instruction set, most simulating subjects failed to recall and recognize autobiographical items. In the first study, an arbitrarily but a priori derived discrimination criterion based on a subject's average P300 amplitude afforded 92% correct discrimination of simulating individual subjects for birthdates and phone numbers. The value was 77% for mothers' maiden names. The same criterion applied to the single birthdate block in the second study yielded 93% correct discrimination. The results suggest the P300 may be useful in detection of malingered amnesia.

The mere exposure effect is based on implicit memory: Effects of stimulus type, encoding conditions, and number of exposures on recognition and affect judgments.

The mere exposure effect is based on implicit memory: Effects of stimulus type, encoding conditions, and number of exposures on recognition and affect judgments.

The mere exposure effect is based on implicit memory: Effects of stimulus type, encoding conditions, and number of exposures on recognition and affect judgments.

The mere exposure effect is based on implicit memory: Effects of stimulus type, encoding conditions, and number of exposures on recognition and affect judgments.

An Experimental Comparison of Stimulus Type, Display Type, and Input Variable Contributions to Visual Field Asymmetry

Three experiments compare the effects of stimulus type, display type, and input variable contributions to visual field (VF) asymmetry. Stimulus types were words and bar graphs; displays were unilateral and bilateral; and input variables were stimulus eccentricity, duration, luminance, and size. The only influences consistent across studies and with claims in the literature were those of stimulus type and display type. Stimulus type determined the direction of VF asymmetry, while display type determined its magnitude. The results suggest that both influences should be accounted for in research using VF asymmetry as an index of hemispheric differences, while input variables can largely be ignored.

Frequency discrimination in the European starling ( Sturnus vulgaris): A comparison of different measures

Frequency-difference limens (DL) were determined in a songbird, the European starling ( Sturnus rulgaris), for stimuli differing in the type of frequency change. Four different types of frequency change were studied: an increase in frequency between pulsed tones (type FSU), a single sinusoidal sweep upward (type SSU) starting in the center of an 800 ms signal, an asymmetrical periodic sinusoidal frequency modulation that extended only above the reference frequency (type ASFM), and a symmetrical periodical sinusoidal frequency modulation extending to both sides of the reference frequency (type SSFM). Frequency DLs at two reference frequencies. 1 and 4 kHz. were studied. At 1 kHz. the starling showed the lowest DL for pulsed tones (11.4 Hz), slightly higher DLs for single sweeps and asymmetrical frequency modulation at modulation frequencies of ≦ 40 Hz (15.9 Hz for stimulus SSU. and 15.3 Hz for low modulation frequencies of stimulus type ASFM). At a reference frequency of 1 kHz. the DL for symmetrical modulation (type SSFM) at modulation frequencies ≦ 40 Hz was about twice as large (21.h Hz) than for pulsed tones. Furthermore, the DLs for periodically modulated signals at a modulation frequency of 320 Hz were about twice as large as those at low modulation frequencies. At a reference frequency of 4 kHz, the differences in the DLs for various stimulus types were insignificant (27.7 Hz for type FSU, 23.3 Hz for type SSU, 28.0 Hz for type ASFM and low modulation frequencies, and 24.6 Hz for type SSFM and low modulation frequencies). Only at high modulation frequencies (≧ 320 Hz) were the DLs increased. The results are discussed with respect to similar effects of stimulus type and reference frequency on the frequency-difference limen in humans and with respect to the frequency DLs in other bird species.

Nonlinearities in binocular visual evoked potentials in children.

Evidence is controversial in respect to the optimal conditions in which visual evoked potentials provide an objective measure of binocular visual function, related and unrelated to stereopsis, and there is little emphasis on the type of stimulus that produces facilitation in binocular recording. We investigated the effects of stimulus type (flicker or pattern), contrast, and temporal modulation on facilitation, which was defined as a binocular response greater than sum of monocular responses. Monocular and binocular responses to sinusoidally modulated flicker and grating patterns were recorded in children and Fourier analyzed. The relationship of the fundamental Fourier component for flicker and the second harmonic component for pattern were each examined as function of temporal modulation at two levels of contrast for monocular and binocular visual evoked potentials. Binocular facilitation was found across all conditions for flicker. Data suggest that processing of pattern and flicker has different sites of origin within the visual system. Facilitation in binocular visual evoked potentials also indicates that they are not a result of simple summation of monocular responses, since there appears a nonlinear component to such interaction.

Distribution of auditory response behaviors in normal infants and profoundly multihandicapped children.

Responsiveness (yes/no decisions) to sound has been found to be similar for normal infants and profoundly multihandicapped children of comparable developmental ages (Flexer & Gans, 1985). The purpose of this investigation is to extend the comparison of these two groups by examining the distribution of their response behaviors to sound. Ten normal and 10 multihandicapped children were videotaped while various auditory signals were presented. Without knowledge of stimulus type, five judges listed the behaviors that occurred during 24 sound and 24 catch trials for each child. The behaviors were then evaluated as a function of the stimulus parameters of meaningfulness, bandwidth, and intensity. Results revealed that the profoundly multihandicapped children displayed relatively more reflexive than attentive type behaviors and exhibited fewer behaviors per response. The effects of stimulus-type on the numbers and distribution of responses are discussed.

The effect of stimulus type and directed attention on dichotic listening with children

This research investigated the effect of stimulus type and directed attention on dichotic listening performance with children. A sample of 12 (5 male, 7 female; mean age 10.5 years) high academically performing children were administered four types of dichotic stimuli (words, digits, CV syllables, and melodies) in three experimental conditions (free recall, directed left, and directed right) to examine perceptual asymmetry as reflected by the right-ear advantage (REA). While the expected REA for words and CV syllables and the expected LEA for melodies were found under free recall, the directed conditions produced varied results depending on the nature of the stimuli. Directed condition had no effect on recall of CV syllables but had a dramatic effect on recall of digits. Word stimuli and directed condition interacted to produce inconsistent perceptual asymmetry while directed condition reduced overall recall for melodies. The findings lend support to the hypothesis that perceptual asymmetries can be strongly influenced by the type of stimulus material used and the effect of attentional strategy employed.

The effects of stimulus type, training, and chronological age on children's identification and recoding of multidimensional stimuli

Kindergarten and second-grade children (75 and 99 months of age, respectively) were first taught that the two stimuli within each of four pairs of multidimentional stimuli differed with respect to their values on every one of three bivalued dimensions: color, size, and form. Each of the eight stimuli was then presented twice, one at a time, and the child was asked either to find its duplicate (eight encoding trials) or to find its complementary mate (eight recoding trials) among the complete set of eight stimuli. Next, each of the eight stimulus compounds was presented twice as a display stimulus for 5 sec and, after a delay of 10 to 15 sec, the child was asked to find the display stimulus (eight trials of encoding plus memory) or its complement (eight trials of recoding plus memory) among the complete set. The stimuli for half the children in each age group were standard unitary compounds (e.g., a large red circle, a small blue square, etc.) and for the other half they were partitioned stimuli with their dimensional values spatially separated (e.g., large arrow, circle outline, and patch of color). Half of the children in each of these subgroups were given a basic pretraining, and the other half received extended pretraining, in recoding the stimulus attributes. The results indicated that unitary stimuli were easier to encode but the partitioned stimuli were easier to recode, that recoding was much more difficult than encoding, that extended training improved recoding performance, and that second graders were slightly better at encoding and much better at recoding than the kindergarten children. The patterns of performance on the tasks involving memory were similar to those just described. The results were discussed in terms of children's abilities to analyze multidimensional stimuli into their dimensional components.

Effects of stimulus duration upon the response characteristics of single neurons in the inferior colliculus of unanesthetized bats (Tadarida brasiliensis mexicana)

Constant frequency (CF) and frequency‐modulated (FM) pulses were utilized to examine the response characteristics of collicular neurons. Tonic, toniclike and various types of phasic “on” responses were noted depending upon the type of stimulus used. For example, a tonic response patten elicited from a given neuron with CF stimulation could be changed to a phasic “on” pattern with FM stimulation. Similarly, thresholds and input—output functions were affected by the stimulus type. Superimposed upon the effects of stimulus type were the effects of stimulus duration. Many neurons were found to have firing patterns and response characteristics to long duration stimuli that differed greatly from those observed with shorter signals having durations less than 2.0 msec. Results suggest that most inferior collicular neurons are best suited for extracting information from signals having durations comparable to those emitted during the search and approach phases of goal‐directed flight and are poorly suited for responding to shorter signals having durations typical of those emitted during the terminal phase of echolocation. [Supported by NSF Grant P401855‐000.]

The effect of stimulus type on formal similarity between stimuli and their primary associations

The experiment investigated the effect of stimulus type on formal similarity (FS) between stimuli and Ss primary associations to them. Word (W) and nonsense (NS) stimuli were employed. FS was defined as percentages of letters appearing in the same ordinal positions in associations as in stimuli. Results indicated that FS between NS stimuli and their primaries consistently exceeded chance while that between W stimuli and their primaries exceeded chance in only one of six cases.

The Effects of Stimulus Type on Performance in a Color-Form Sorting Task with Preschool, Kindergarten, First-Grade, and Third-Grade Children

The Effects of Stimulus Type on Performance in a Color-Form Sorting Task with Preschool, Kindergarten, First-Grade, and Third-Grade Children