Visual field differences in the processing of numerical stimuli

Twenty-four right-handed subjects received random presentations of the numbers 1-6 in the form of words, digits, and dot patterns, to the left and right visual fields. Accuracy and reaction time were recorded for an odd-even judgment requiring a manual response. A significant stimulus type of visual field interaction was obtained, with words showing a left-hemisphere advantage and digits and dot patterns showing a right-hemisphere advantage. This pattern supports Coltheart's (1980, Deep dyslexia: A right hemisphere hypothesis, In M. Coltheart, K. Patterson, & J.C. Marshall (Eds.), Deep dyslexia, London: Routledge & Kegan Paul) right hemisphere reading hypothesis, which suggests that the left hemisphere's general advantage in processing linguistic material may be specific to stimuli which involve phonological processing. When phonological processing is not possible (e.g., for arabic digits and other ideographic orthographies), the right hemisphere may have an advantage because of its superior visuospatial processing capabilities.     

Perceptual identification of visually degraded stimuli

In this article, we describe procedures, materials, and some representative results of a microcomputer-based approach to the degradation of visual stimuli for the investigation of perceptual identification. We discuss application of the procedures for the production of visually degraded picture, letter, and word stimuli, and of visual stimuli common to neuropsychological investigations.     

Impulsivity and perception: individual differences in the processing of the local and global dimensions of stimuli

There appears to be an association between a "global" mode of perceptual processing and a cluster of personality traits, one of which is impulsivity. The goal of the present study was to clarify this relationship. Subjects differing in impulsivity (as measured by a self-report inventory) performed speeded cardsorting tasks. They sorted stimuli consisting of large letters made up of smaller letters. Highly impulsive subjects had no more difficulty than other subjects in ignoring the large, "global," letters when they tried to attend to the smaller, "local," letters of which they were composed, nor were they more vulnerable than other subjects to Stroop-like response interference produced by the global letters. High impulsives did have particular difficulty when the task required that they integrate the information provided by the local and global letters. This finding can be explained in terms of individual differences in the value placed on speed relative to accuracy in information processing.     

Sex differences in categorization of tactile stimuli

This experiment investigated the effect of sex differences in categorization of tactile stimuli. 9 men and 9 women rated the perceived similarity between pairs of stimuli varying in texture and shape. The magnitudes of sex-related differences, using omega 2 and d, were relatively large and indicated that men had better categorical abilities in processing haptic information.     

Parallel processing of multidimensional stimuli

A reaction time (RT) task in which S is required to judge pairs of stimuli either the same or different was used in three experiments in order to determine the processing mode employed in complex discriminations. The results of all experiments indicated that stimulus dimensions are processed by parallel but not necessarily independent analyzers.     

Comparing perception of Stroop stimuli in focused versus divided attention paradigms: Evidence for dramatic processing differences

A huge set of focused attention experiments show that when presented with color words printed in color, observers report the ink color faster if the carrier word is the name of the color rather than the name of an alternative color, the Stroop effect. There is also a large number (although not so numerous as the Stroop task) of so-called “redundant targets studies” that are based on divided attention instructions. These almost always indicate that observers report the presence of a visual target (‘redness’ in the stimulus) faster if there are two replications of the target (the word RED in red ink color) than if only one is present (RED in green or GREEN in red). The present set of four experiments employs the same stimuli and same participants in both designs. Evidence supports the traditional interference account of the Stroop effect, but also supports a non-interference parallel processing account of the word and the color in the divided attention task. Theorists are challenged to find a unifying model that parsimoniously explains both seemingly contradictory results.     

Developmental differences in response processing

Three age groups (kindergartners, fourth graders, and adults) were compared in their processing of response decisions in a two-choice reaction time task. Manipulation of spatial stimulus-response compatibility resulted in age-related differential effects on reaction time performance. For the younger children, selecting the appropriate response for an incompatibly paired stimulus light required proportionately longer processing time than for older subjects. Similar results were not found for performance under varying levels of response discriminability.     

Gender differences in phonetic processing

In research on dyslexia, inadequate or inappropriate comparisons have often been made with control subjects, frequently overlooking important gender differences. More information is needed regarding the performance of control subjects, and adults, on measures purportedly assessing phonological and orthographic processing. Using tests similar to those used in dyslexic research, 20 female and 20 male college-age students were tested to examine gender differences in phonetic processing skills. The findings suggest that in equally competent readers, gender and other factors do play a significant role in determining the time it takes for phoneme manipulation and word identification. Females, especially those with poorer academic records, are significantly slower than males on measures typically used in dyslexic research. These findings show a need for a reexamination of control group equivalence (especially regarding gender), and further exploration of variables that might influence performance on these tasks.     

Sex differences in information processing

Sex differences in cognitive activity were investigated. Using a list containing words with masculine, feminine, and neutral connotations, Experiment 1 revealed that masculine words were better recalled by male college students (n=16) while feminine words were better recalled by female college students (n=16). This difference was reduced on a recognition test. Experiment 2 demonstrated that the phenomenon was not due to a difference in the way males (n=20) and females (n=20) interpreted the meaning of the words. Finally, in Experiment 3, the memorial selectivity was shown to exist in the same manner for White middle-class elementary school (n=32) and high school (n=32) students. Learning and repression interpretations of the effect were proposed. Some practical implications of the data were suggested.These investigations were supported by a seed grant to the first author. This grant was jointly funded by Southern Methodist University and the National Science Foundation's Institutional Grants for Science Program (GU-3752). The authors would like to express their appreciation to the pupils and teachers on Fain Elementary School and Rider High School, both in Wichita Falls, Texas.     

Hemispheric differences in case processing

Morphosyntactic capacities of normal brain hemispheres were compared in lexical decision studies involving centrally and laterally presented Serbo-Croatian nouns in different cases. Cases are distinguished by different suffixes and syntactic roles. Experiment 1 confirmed and extended previous findings of the nominative superiority effect: words in the nominative case were processed faster and more accurately than words in other three cases, and nonwords in the nominative case led to more false positive reactions than nonwords in other cases. In Experiment 2 this effect was replicated for right visual field stimuli: nominatives had faster reaction times and smaller error rates than accusatives, and the reversed pattern was found for nonwords. For left visual field stimuli, only the word error analysis found the nominative superior, while the other three analyses (word reaction times, nonword reaction times, and nonword error rates) showed no significant case effect. Word familiarity had an equally strong effect in both hemispheres. The results suggest that centrally presented stimuli are processed by the left hemisphere, that laterally presented stimuli are processed by the initially receiving hemisphere, and that the right hemisphere has a frequency-sensitive lexicon. Reduced right-hemisphere sensitivity for case differences may be due to different lexicon structure or the absence of appropriate morphological or syntactic mechanisms.     

Gender differences in phonetic processing

In research on dyslexia, inadequate or inappropriate comparisons have often been made with control subjects, frequently overlooking important gender differences. More information is needed regarding the performance of control subjects, and adults, on measures purportedly assessing phonological and orthographic processing. Using tests similar to those used in dyslexic research, 20 female and 20 male college-age students were tested to examine gender differences in phonetic processing skills. The findings suggest that in equally competent readers, gender and other factors do play a significant role in determining the time it takes for phoneme manipulation and word identification. Females, especially those with poorer academic records, are significantly slower than males on measures typically used in dyslexic research. These findings show a need for a reexamination of control group equivalence (especially regarding gender), and further exploration of variables that might influence performance on these tasks.     

Developmental differences in shape processing

Considerable evidence indicates that shape similarity plays a major role in object recognition, identification and categorization. However, little is known about shape processing and its development. Across four experiments, we addressed two related questions. First, what makes objects similar in shape? Second, how does the processing of shape similarity develop? We specifically asked whether children and adults determine shape similarity by using categories (e.g., straight vs. curved), as proposed by Biederman (1987), or whether they treat all shape variability uniformly, as proposed by Ullman (1998). Findings from Experiments 1 and 2 suggest that adults and 7-year-olds generally engage in a process in which they impose categories on shape variation and judge objects that fall within those categories as being similar in shape. Four-year-olds are far less likely to engage in such a process. Experiments 3 and 4 address whether 4-year-olds are more likely to treat shape similarity categorically (as older children and adults do) when the objects are given familiar names, functions, and internal properties. Naming did lead to more advanced treatment of shape similarity in some cases. Overall, these findings provide evidence of developmental differences in shape processing and suggest that knowledge of abstract properties of objects may affect the calculation of shape similarity.     

Anxiety-related differences in affective categorizations of lexical stimuli

Effects of emotional valence on attention have been shown to occur even when stimuli are presented outside awareness. The impact of negative valence on stimulus processing has been demonstrated to be particularly salient in anxiety. Therefore, it has been hypothesized that compared to nonanxious individuals, anxious individuals have an enhanced ability to detect the valence of negative stimuli. However, it remains unclear whether anxious individuals are better at identifying the valence of threatening stimuli or, rather, more likely to label ambiguous stimuli as threatening. To investigate these hypotheses, high and low anxious participants categorized lexical stimuli as "safe" or "dangerous." Stimuli were presented at durations that allowed for both conscious (unmasked) and nonconscious (masked) processing. Results show that on masked trials, anxious individuals evidenced an enhanced ability to correctly classify threatening information, whereas nonanxious participants demonstrated an enhanced ability to correctly classify neutral or positive information. Signal detection analyses indicated results were explained by a response bias, whereby anxious individuals were more likely than nonanxious individuals to categorize masked words as threatening and nonanxious individuals were more likely to categorize masked words as nonthreatening. No group differences for nonword stimuli emerged, suggesting that anxiety-related response bias tendencies are activated only after detection of a weak semantic signal.     

Age-related differences in the pleasantness of chemosensory stimuli

Modest decrements in both taste threshold sensitivity and, more recently, suprathreshold sensitivity have been associated with the aging process. The present study was designed to investigate the existence of changes in preference for various concentrations of single tastes and of the same single tastes in more complex chemosensory mixtures. In this study, 300 participants from three different age groups (18-26, 32-45, over 65) rated for pleasantness four concentrations of sodium chloride, sucrose, and citric acid presented in both aqueous and beverage bases. Results showed significant effects of age, stimulus background, stimulus, concentration, and of several interactions, and they suggest that elderly subjects find salt and sugar pleasanter at higher concentrations than younger subjects do.     

Low-frequency filtering and the processing of local-global stimuli

The role of low-spatial-frequency information in the processing of global stimuli made up of local elements was examined. After selective removal of low spatial frequencies two major changes occurred in the pattern of results. First, response times to global stimuli were significantly slower and the usual speed advantage of global over local processing was lost. Second, when processing local features the usual decrease in response speed when the local and global letters are not the same (consistency effect) was not obtained. These effects could not be explained by changes in error rate, by contrast variation resulting from the process of filtering, or by loss of visual sensitivity due to greater eccentricity of global images.     

Task-dependent costs in processing two simultaneous auditory stimuli

A listener presented with two speech signals must at times sacrifice the processing of one signal in order to understand the other. This study was designed to distinguish costs related to interference from a second signal (selective attention) from costs related to performing two tasks simultaneously (divided attention). Listeners presented with two processed speech-in-noise stimuli, one to each ear, either (1) identified keywords in both or (2) identified keywords in one and detected the presence of speech in the other. Listeners either knew which ear to report in advance (single task) or were cued afterward (partial-report dual task). When the dual task required two identification judgments, performance suffered relative to the single-task condition (as measured by percent correct judgments). Two different tasks (identification for one stimulus and detection for the other) resulted in much smaller reductions in performance when the cue came afterward. We concluded that the degree to which listeners can simultaneously process dichotic speech stimuli seems to depend not only on the amount of interference between the two stimuli, but also on whether there is competition for limited processing resources. We suggest several specific hypotheses as to the structural mechanisms that could constitute these limited resources.     

Information processing in imagination using nonverbalizable visual stimuli

In groups of 20 to 25, 146 undergraduates were tested as to their ability to mentally combine two shapes. They were to pick the correct choice from 5, 7, 9, 11, 13, or 15 alternatives. The shapes were previously proven to be effectively unverbalizable but recognizable and discriminable. Contrary to expectation, there was no negative decrement in performance with increasing numbers of incorrect alternatives.     

Directional scanning and cerebral asymmetries in processing visual stimuli.

A perceptual exploration task involving three horizontal linear arrays of stimuli was administered to 167 children ranging in age from 3 to 7 yr. It was found that the well organized, predominantly right-to-left responses of very young children were eventually replaced by left-to-right patterns. A tachistoscopic test showed that Ss who gave right-to-left responses to the linear arrays showed hemispheric asymmetry of perception. The results were interpreted as supporting the view that directional response tendencies are related to hemispheric asymmetry.