Apractic agraphia in a patient with normal praxis

Most right-handed crossed aphasics are not apractic. They usually have agraphia characterized by misspellings but retain the ability to write well-formed graphemes. We describe a right-handed patient with a right parietal lesion who was aphasic and not apractic. He was unable to write any formed graphemes despite a relatively preserved ability to spell aloud. We postulate that praxis and writing are dissociated in this patient because the motor engrams for praxis were located in his left hemisphere and the engrams for writing were in his right hemisphere. In addition, he comprehended commands for limb motor activities (praxis) far better than he comprehended other speech. This suggests that in this patient the areas used to comprehend limb motor commands may be anatomically distinct from areas important in comprehending other aspects of speech.     

The Assessment of Limb Apraxia: An Investigation of Task Effects and Their Cause

To test the effects of variations in the structure of tasks used to assess limb apraxia, eight tasks—differing in their modes of elicitation (tactile, verbal, visual, imitation) and/or types of movement elicited (transitive, intransitive, meaningless)—were administered to 25 carefully selected subjects with idiomotor limb apraxia. When standardized scores (based on the performance of 10 nonneurologically impaired control subjects) were used to measure the differences between tasks, no clinically significant task effects were found. Additional investigation was made of two causal hypotheses regarding the processes underlying limb apractic performance. The results of factor analyses and a search for double dissociations among individual subjects were consistent with the (severity) hypothesis that differences in task performances (raw scores) reflect degrees of task difficulty; and they failed to support the (disconnection) hypothesis that posits separate and independent neural/mental processes underlying task performances.     

Nonspeech and speech processing skills in patients with aphasia and apraxia of speech

Nonspeech and speech auditory processing skills as well as internal speech processing skills were assessed among four patients with acquired "pure" apraxia of speech, 10 with acquired aphasia, 10 with aphasia plus apraxia of speech, and 11 neurologically normal adults. Fourteen tasks were administered and performances on 68 variables were examined using both nonparametric and parametric analyses controlling for the effects of advancing age and associated hearing loss. In all cases, the "pure" apractic patients performed as normal subjects. Few differences were noted among the performances of the aphasic and aphasic-apractic subjects. Results led to three major conclusions: (1) apraxia of speech is a disorder distinct from aphasia; (2) aphasic individuals, despite locus of lesion, demonstrate disabilities for processing nonspeech and speech materials presented auditorily and for analytically evaluating speech evoked internally; and (3) aphasic individuals demonstrating similar severity levels of language impairment show similar performance patterns for these types of processing tasks, despite locus of lesion or coexistence of apraxia of speech.     

Toward a theory of apractic syndromes

Theoretical development on human motor behavior has occurred largely independently of data on pathological movement disorders. This paper represents an initial attempt to interface findings from studies of apraxia and those of normal motor behavior with a view to formulating a common theoretical framework. Such an integration may ultimately aid in understanding the nature of skill acquisition and provide insights into the organization of motor systems. Three putative theoretical models of movement control are discussed with reference to apractic syndromes. The most commonly accepted view—the hierarchy—possesses properties such as linear transitivity and unidirectionality of information flow that render it inadequate in explaining functional plasticity in the central nervous system. The heterarchy, which incorporates reciprocity of function and circular transitivity, is a more likely candidate but suffers from an inability to regulate the degrees of freedom of the system. Our favored candidate is the coalition model which embodies heterarchical principles, but in addition, offers a solution to the problems of degrees of freedom and context for motor systems. Evidence is reviewed from apraxia of speech and limbs in terms of a coalitional style of control and an experimental approach, consonant with coalitional organization, is developed. We promote the claim that an understanding of apractic behavior—and perhaps motor systems in general—will benefit when clinicians and experimenters embrace a theory of context and constraints rather than a theory of commands as is currently in vogue.     

The effect of vicarious reinforcement on attentive behavior in the classroom

The effect of social reinforcement delivered to target subjects on the attentive behavior of adjacent peers was examined in a classroom setting. In a combined reversal and multiple baseline design, two pairs of mentally retarded children were sequentially exposed to three reinforcement phases. After baseline rates of attentive behavior were obtained, praise was delivered to the target subject in each subject pair for attentive behavior. After a reversal phase, praise was delivered contingently to target subjects for inattentive behavior. In a final phase, contingent praise for attentive behavior was reinstated for the target subjects. Throughout the study, nontarget subjects received no direct reinforcers. The results indicated a vicarious reinforcement effect. Reinforcing attentive behavior of target subjects increased this behavior in adjacent peers. However, reinforcing inattentive behavior of target subjects also increased the attentive behavior of adjacent peers. The effects obtained through vicarious reinforcement were considered to reflect the discriminative stimulus properties of reinforcement, which may serve as a cue for the performance of nonreinforced peers.     

Semantic category effects in visual word search

The initial question was whether subjects could categorize a word semantically before they precisely identified the word itself. This failed to occur. When searching a visual display for a single target word, subjects searched at the same rate whether the distractors were in the same or in a different semantic category. However, when the size of the target set was increased to three, then six, items, subjects increasingly used category information to speed their search rate when targets and distractors belonged to different categories. Subjects appeared to perform the task by comparing the category of each display word to the category of the target set.     

Effects of salience and time pressure on ratings of social causality

A model is proposed to account for the effects of a target person's salience on judgments of that target. It is argued that salience leads to more extreme inferences in the direction implied by prior knowledge that is relevant to the judgment. This knowledge may include both specific information about the target being rated and general information about the class of stimuli to which the target belongs. Two experiments supported these hypotheses. When subjects were under time pressure to make judgments of a target person's influence in a social situation, their judgments increased with the salience of the target when they had prior knowledge that the target was generally high in social influence. However, their judgments decreased with the target's salience when subjects had prior knowledge that the target was generally low in social influence. When subjects were given ample time to make their judgments, however, the effects of target salience were attenuated. Possible implications of these findings for prior research on salience effects are discussed.     

AN EXPERIMENTAL ANALYSIS OF “SPILLOVER” EFFECTS ON THE SOCIAL INTERACTION OF BEHAVIORALLY HANDICAPPED PRESCHOOL CHILDRENsp1

The effects of prompting and social reinforcement directed to target subjects on their social behavior and that of peers who never received prompting and reinforcement for positive social behavior, were examined. In a combined reversal and multiple-baseline design, three behaviorally handicapped preschool boys who exhibited divergent social behavior repertoires and varied histories with social reinforcement events, were sequentially exposed to intervention conditions in order to investigate “spillover” of treatment effects. Prompting and reinforcement increased positive social behavior and decreased negative social behavior emitted by all target subjects. The results also demonstrated a “spillover” effect on two target subjects, who at various times were not under intervention, and on the peers as well. The findings suggest that: (a) the direct and indirect effects of intervention procedures may be enhanced by designing treatment based on the social repertoire and reinforcement histories of the subjects; and (b) the treatment “spillover” effect may be increased by applying procedures to two children at once, rather than to one at a time.     

Early and late selection in partial report: Evidence from degraded displays

In studies of iconic memory using the bar-probe task, subjects see a brief display of target letters and are probed by an arrow to report one of them. According to the classic early-selection account, subjects use the probe to select material for perceptual analysis from a precategorical (iconic) memory, but according to late-selection theories, subjects first identify the letters and then use the probe to select one letter for report from the set of categorized items. Pashler (1984) based his test for the locus of selection on a manipulation of display quality in previewed displays. He presented a target for 200 msec and then added a probe, together with the target, for an additional 150 msec. Reducing the target’s stimulus quality increased response latency. If the subjects identified the characters before the probe appeared and then selected an item for report, the clarity of the original array should not have affected response latency. Hence, Pashler concluded that his subjects used the probe to select from a precategorical store (early selection). Pashler’s experiment did not force subjects to rely on memory of the target; hence, although his experiment documented a situation in which subjects used early selection, it did not rule out late selection in studies of information persistence. We replicated Pashler’s findings and, using his logic, showed that when subjects are forced to rely on memory of the target, they select from a categorized store.     

Influence of item identification on the memory performance of mentally retarded and nonretarded adults

The role of item identification in the memory performance of mentally retarded and nonretarded adults was examined by varying the identification and memory parameters of a sequential same-different task. In Study 1, retarded subjects' identification ability was demonstrated to be less efficient than nonretarded subjects' ability. In Study 2, target duration and interstimulus interval were varied. Memory performance differed between groups, and the memory deficit for retarded subjects was demonstrated to be independent of their identification deficit. The target durations in Study 2 were relatively brief, and in Study 3, the target duration was increased to insure that all subjects could identify the target. Mentally retarded subjects were demonstrated to have a memory deficit. The results were discussed in terms of possible sources of the memory deficit.     

Early and late selection in partial report: evidence from degraded displays.

In studies of iconic memory using the bar-probe task, subjects see a brief display of target letters and are probed by an arrow to report one of them. According to the classic early-selection account, subjects use the probe to select material for perceptual analysis from a precategorical (iconic) memory, but according to late-selection theories, subjects first identify the letters and then use the probe to select one letter for report from the set of categorized items. Pashler (1984) based his test for the locus of selection on a manipulation of display quality in previewed displays. He presented a target for 200 msec and then added a probe, together with the target, for an additional 150 msec. Reducing the target's stimulus quality increased response latency. If the subjects identified the characters before the probe appeared and then selected an item for report, the clarity of the original array should not have affected response latency. Hence, Pashler concluded that his subjects used the probe to select from a precategorical store (early selection). Pashler's experiment did not force subjects to rely on memory of the target; hence, although his experiment documented a situation in which subjects used early selection, it did not rule out late selection in studies of information persistence. We replicated Pashler's findings and, using his logic, showed that when subjects are forced to rely on memory of the target, they select from a categorized store.     

Control of fixation duration in a simple search task

To obtain insight into the control of fixation duration during visual search, we had 4 subjects perform simple search tasks in which we systematically varied the discriminability of the target. The experiment was carried out under two conditions. Under the first condition (blocked), the discriminability of the target was kept constant during a session. Under the second condition (mixed), the discriminability of the target varied per trial. Under the blocked condition, fixation duration increased with decreasing discriminability. For 2 subjects, we found much shorter fixation durations in difficult trials with the mixed condition than in difficult trials with the blocked condition. Overall, the subjects fixated the target, continued to search, and then went back to the target in 5%–55% of the correct trials. In these trials, the result of the analysis of the foveal target was not used for preparing the next saccade. The results support a preprogramming model of the control of fixation duration. In a simple search task, control of fixation duration appears to be indirect.     

Masked orthographic priming in bilingual word recognition

Two lexical decision experiments tested the influence of briefly presented orthographically related primes on target word recognition in bilinguals. The prime stimuli were high-frequency words either from the same language as that of the target or from the other language known by the bilingual subjects. When the prime and target were from the same language, orthographically related primes systematically inhibited target word recognition, whereas orthographically dissimilar primes did not. When the prime and target were words from different languages, the amount of inhibition increased as a function of subjects’ level of proficiency in the prime word’s language, with highly proficient bilinguals showing practically equivalent amounts of within and across language inhibitory priming. These results strongly suggest that a printed string of letters can simultaneously activate lexical representations in both of the bilingual’s languages (insofar as these share the same alphabet), even when subjects are performing a monolingual task.     

What is learned about nontarget items in simple visual search?

Human sensitivity to correlational structure between nontargets and likelihood of target presence in a visual letter-search task were studied in two experiments. In each of these experiments, the performance of subjects for whom the nontarget information was altered in the final trial block was compared with the performance of subjects for whom the nontarget information did not change. When stimulus strings were presented individually on a computer screen and subjects were required to make a yes-no decision about target presence (Experiment 1), the change in nontarget structure resulted in increased reaction times for target-absent trials. When subjects searched simultaneously for three possible targets (Experiment 2), the change in nontarget structure produced increased error rates and increased reaction times for both target-absent and target-present trials. Correlations between the amount of predictive information in individual stimulus strings and reaction times also showed that both switching and nonswitching subjects were sensitive to the nontarget context. However, neither self-reports of strategy nor postexperiment choices between context-consistent and -inconsistent letter strings indicated any explicit knowledge of the predictive information in the nontarget stimuli. Subjects can thus acquire and benefit from, apparently without awareness, information about subtle correlational structure in nontarget elements in simple visual search.     

Submovement Organization,Pen Pressure,and Muscle Activity Are Modulated to Precision Demands in 2D Tracking

The authors investigated how tracking performance, submovement organization, pen pressure and muscle activity in forearm and shoulder muscles were affected by target size in a 2D tracking task performed with a pen on a digitizer tablet. Twenty-six subjects took part in an experiment, in which either a small dot or a large dot was tracked, while it moved quasirandomly across a computer screen at a constant velocity of 2 cm/s. The manipulation of precision level was successful, because mean distance to target and the standard deviation of this distance were significantly smaller with the small target than with the large target. With a small target, subjects trailed more behind the center of target and used submovements with larger amplitudes and of shorter duration, resulting in higher tracking accuracy. This change in submovement organization was accompanied by higher pen pressure, while at the same time muscle activity in the forearm extensors and flexors was increased, indicating higher endpoint stability. In conclusion, increased precision demands were accommodated by both a different organization of submovements and higher endpoint stability in a 2D tracking task performed with a pen on a digitizer tablet.     

Processing differences between memory search and foveal visual search

The ability to detect small differences in the positions of two lines (vernier acuity) showed some improvement with practice in all eight subjects, even for subjects given no error feedback. The average decline in threshold with training (2,000–2,500 responses) was about 40%. We used three target orientations: vertical, horizontal, and right oblique. Orientational differences remained stable in only one subject. In five subjects, orientational differences present at the beginning of training diminished or disappeared with increased experience; in two, they increased.     

The intrusiveness of familiar nontarget information

Two experiments required subjects to attend to one of two binaurally presented passages and, at the same time, perform a visual reaction time (RT) task. Mean RT measured the capacity expended on selective listening: Longer RTs imply greater capacity expenditure. The relative familiarity of target and nontarget passages and the cue by which they could be differentiated (sensory vs. semantic) were manipulated. The target passages were defined by the experimenter in Experiment 1 but chosen by the subjects in Experiment 2. Both experiments showed that expenditure of capacity increased from sensory to semantic selection and increased with non-target familiarity only for semantic selection. The data were interpreted in terms of a multi-mode theory of attention.     

Searching for conjunctively defined targets

It has recently been proposed that in searching for a target defined as a conjunction of two or more separable features, attention must be paid serially to each stimulus in a display. Support for this comes from studies in which subjects searched for a target that shared a single feature with each of two different kinds of distractor items (e.g., a red O in a field of black Os and red Ns). Reaction time increased linearly with display size. We argue that this design may obscure evidence of selectivity in search. In an experiment in which the numbers of the two distractors were unconfounded, we find evidence that subjects can search through specified subsets of stimuli. For example, subjects told to search through just the Os to find the red O target do so without searching through Ns. Implications of selective search are discussed.     

正常高值血压者血压昼夜节律与靶器官损害的相关性研究

探讨正常高值血压昼夜节律与靶器官损害的相关性。入选正常高值血压者150例,其中杓型组72例,非杓型组78例,60例正常血压者为对照组。检测尿白蛋白排泄率（UAE）、颈动脉内膜中层厚度（IMT）和左心室重量指数（LVMI）。杓型组和非杓型组UAE、IMT、LVMI高于对照组（P＜0．01）。非杓型组UAE、IMT、LVMI高于杓型组（P＜0．05）。正常高值血压人群已出现靶器官损害,血压昼夜节律异常与早期靶器官损害密切相关。     

Vowel recognition: Inferences from studies of forward and backward masking

The recognition of brief vowels was studied in forward and backward masking tasks. In a series of experiments in which both target and mask parameters were systematically varied, two populations of subjects were identified. The majority (Nonmaskers) evidenced little masking at any interstimulus interval, while relatively fewer subjects (Maskers) evidenced backward masking (but not forward masking) over a 100-200 ms interval. Increasing target set size systematically increased masking for the Maskers but not for the Nonmaskers. Adding white noise to the targets increased the extent of masking for both groups. These results suggest (1) that masking does not impose a substantive constraint on vowel perception in running speech, and (2) that multiple strategies may exist for vowel recognition.