A note on sequential blanking

Five-letter pseudowords were presented in all possible spatiotemporal orders at each of nine combinations of letter duration and interletter interval. Subjects were required to report as many letters of the pseudoword as possible. The results confirmed the sequential blanking effect; under certain timing conditions, some spatiotemporal orders result in perceptual blanking. The results show, however, that blanking does not follow the two rules previously thought to describe the phenomenon.     

Visual cortical evoked potentials under conditions of sequential blanking

Two separate experiments were conducted to study the visual evoked potential (VEP) correlates of sequential blanking, a phenomenon in which up to one-half of a discrete train of stimulus inputs are not perceived for certain orders of input. A PDP-7 digital computer was used to present stimuli (from 2 to 5 letter Xs) on a CRT display in both experiments. In Experiment 1 there were four basic conditions designed and counterbalanced to indicate the nature of the VEP when stimuli were blanked and when Ss reported all stimuli. All of the stimuli were of equal intensity. The main finding was that although the eight Ss did not perceive and report blanked stimuli, they did respond to them physiologically as indicated by the VEP. The implications of these findings were discussed in relation to recent studies of visual masking and metacontrast in which VEP was recorded. In Experiment 2 the normally blanked and the normally blanking stimuli were alternately increased in intensity to determine the effect on sequential blanking and the VEP. Six Ss were tested under three basic counterbalanced conditions. It was found that sequential blanking could be reliably overcome by increasing the intensity of the normally blanked stimuli. In addition, when the normally blanking stimuli were of greater intensity than the blanked stimuli, not only did perceptual suppression occur, but the evidence indicated that there was no VEP to the first of the two blanked stimuli.     

A CRT blanking circuit for video terminals

A simple and inexpensive modification for the ADDS 980 video terminal is described which permits the characters displayed on the CRT to be blanked and restored (under software control). This circuit is useful in applications, such as RT measurement, where precise definition of stimulus onset is important. The technique described is general enough to be applied to a variety of other video terminals.     

The rate of word integration and the overprinting paradigm

In the first experiment, the letters of words were overprinted; that is, successive letters were presented on the same location of the screen. Word identification was difficult unless the rate of presentation was slow, about 3 letters/sec. The second experiment showed that the low level of word identification did not reflect difficulty with basic letter identification. Instead, it reflected the rate at which short-term memory can accept separate items. While such results refute models of reading that stress a letter-by-letter integration, they do not test those that stress construction of higher order units. Instead, the task forces letter-byletter integration by removing spatial information, a dimension required for construction of higher order units. As a result, it does not permit integration of the correct units. The third experiment illustrated the construction and integration of supraletter units. Letter groups (either syllables or corresponding nonsyllable groups! were overprinted, a technique that introduces the spatial dimension. Word identification increased dramatically, and subjects were able to exploit the familiarity inherent in syllabic presentations. Thus, integration is much faster when more appropriate units can be used, and construction of the units depends on spatial information. The fourth experiment showed that the construction of supraletter units is achieved prior to short-term memory: Even though memory was able to group the material, the subjects could not use syllabic structure when syllables were isolated temporally but not spatially. The results were discussed in terms of a model describing the construction of higher order units.     

A detailed study of sequential saccadic eye movements for normal- and poor-reading children

This paper presents the results of an in-depth study of parameters characterizing sequenced saccadic eye movements for a group of dyslexic children and a comparative normal control group with ages in the range greater than 8.0 yr. and less than 13.0 yr. No parameters were statistically different for the two groups, which supports the findings of Brown, et al. and contradicts the findings of Pavlidis. Our results indicate that sequenced saccadic eye movements are not diagnostically useful for early detection of dyslexia.     

CLASSI: A classification model for the study of sequential processes and individual differences therein

In psychological research, one often aims at explaining individual differences in S-R profiles, that is, individual differences in the responses (R) with which people react to specific stimuli (S). To this end, researchers often postulate an underlying sequential process, which boils down to the specification of a set of mediating variables (M) and the processes that link these mediating variables to the stimuli and responses under study. Obviously, a crucial task is to chart how the individual differences in the S-R profiles are caused by individual differences in the S-M link and/or by individual differences in the M-R link. In this paper we propose a new model, called CLASSI, which was explicitly designed for this task. In particular, the key principle of CLASSI consists of reducing the S, M, and R nodes of a sequential process to a few mutually exclusive types and inducing an S-M and an M-R person typology from the data, with the S-M person types being characterized in terms of if S type then M type rules and the M-R person types in terms of if M type then R type rules. As such, the S-M and M-R person types and their associated if–then rules represent the important individual differences in the S-M and M-R links of the sequential process under study. An algorithm to fit the CLASSI model is described and evaluated in a simulation study. An application of CLASSI to data from the behavioral domain of anger and sadness is discussed. Finally, we relate CLASSI to other methods and discuss possible extensions. The first author is a post-doctoral fellow of the Fund for Scientific Research—Flanders (Belgium). The research reported in this paper was partially supported by the Research Council of K.U. Leuven (GOA/05/04).     

A sequential theory of psychological discrimination

A theory of discrimination which assumes that subjects compare psychological values evoked by a stimulus to a subjective referent is proposed. Momentary differences between psychological values for the stimulus and the referent are accumulated over time until one or the other of two response thresholds is first exceeded. The theory is analyzed as a random walk bounded between two absorbing barriers. A general solution to response conditioned expected response times is computed and the important role played by the moment generating function (mgf) for increments to the random walk is examined. From considerations of the mgf it is shown that unlike other random walk models [Stone, 1960; Laming, 1968] the present theory does not imply that response conditioned mean correct and error times must be equal. For two fixed stimuli and a fixed referent it is shown that by controlling values of response thresholds, subjects can produce Receiver Operating Characteristics similar or identical to those predicted by Signal Detection Theory, High Threshold Theory, or Low Threshold Theory.     

A chart review study of the inattentive and combined types of ADHD

Studies of the clinical correlates of the subtypes of Attention-Deficit/Hyperactivity Disorder (ADHD) have identified differences in the representation of age, gender, prevalence, comorbidity, and treatment. We report retrospective chart review data detailing the clinical characteristics of the Inattentive (IA) and Combined (C) subtypes of ADHD in 143 cases of ADHD-IA and 133 cases of ADHD-C. The children with ADHD-IA were older, more likely to be female, and had more comorbid internalizing disorders and learning disabilities. Individuals in the ADHD-IA group were two to five times as likely to have a referral for speech and language problems. The children with ADHD-IA were rated as having less overall functional impairment, but did have difficulty with academic achievement. Children with ADHD-IA were less likely to be treated with stimulants. One eighth of the children with ADHD-IA still had significant symptoms of hyperactivity/impulsivity, but did not meet the DSM-IV threshold for diagnosis of ADHD-Combined Type. The ADHD-IA subtype includes children with no hyperactivity and children who still manifest clinically significant hyperactive symptomatology but do not meet DSM-IV criteria for Combined Type. ADHD-IA children are often seen as having speech and language problems, and are less likely to receive medication treatment, but respond to medical treatment with improvement both in attention and residual hyperactive/impulsive symptoms.     

A control theory of sequential response production

Summary Response bias as it occurs in sequential response production, especially in response randomization tasks, is an intriguing problem. The strength theory, which predicts that responses are produced because of their strength or availability in memory, can explain only a fraction of the phenomena of response bias. Two other theoretical approaches need special attention. The first is the concept hypothesis which suggests that response bias is the result of subjective randomness in producing a random sequence. The second is the control hypothesis which suggests that response bias is the result of attempts on the part of the subjects to control perseverations and stereotypes.Unfortunately, there is a lack of experimental evidence to support the concept hypothesis in randomization. The control hypothesis seems a better theory for explaining various instances of response bias. An additional theoretical advantage of the control hypothesis is that it can also explain response bias in areas of sequential response bias other than randomization.     

Improvement of arithmetic self concept through combined positive reinforcement, peer interaction, and sequential curriculum

This study investigated the development of arithmetic self concept and achievement among seven- to nine-year-old children who had problems or who were at the bottom of the lowest track of a third grade. Ss were two girls and two boys from a class of 24 low track children, who completed a one-dimensional five-point scale for self concept and were administered 20-item tests for achivement in arithmetic repeatedly throughout eight weeks of instruction. Formation of small groups, peer interaction, individual curriculum adjustment, and positive reinforcement both at individual and group level were applied. Effective, correlated results were recorded along both scales for each child, and the gains for the four target children were shown in comparison to the class as a whole.     

SDIS: A sequential data interchange standard

Few general-purpose computer programs are available that analyze sequential categorical data. If there were a sequential data interchange standard—a standard way of representing sequential data—then it would be more attractive to write general-purpose computer programs for such data Moreover, interlaboratory sharing would be facilitated. The present paper defines such a standard, called the sequential data interchange standard, or SDIS. Both the SDIS data language and a parsing program for data that follow SDIS conventions are described. The parsing program will be made available to researchers who wish to develop analysis programs for sequential data     

Different effects of eyelid blinks and target blanking on saccadic suppression of displacement

Displacements of visual stimuli during saccadic eye movements are often not noticed. We have demonstrated that saccadic suppression of image displacement can be eliminated by blanking the stimulus for a short period during and after the saccade (Deubel, Schneider, & Bridgeman, 1996). Here we report an experiment in which target visibility was interrupted after the saccade, either by distal target blanking or by voluntary eyeblink. The data show that the effect of blinking is different from blanking; interruption of vision due to a blink did not enable subjects to detect target displacements any better than they had done in the no-blank condition. The results provide evidence for an extraretinal signal that distinguishes between endogenous and exogenous sources of temporary object disappearance after the saccade.     

A quantitative analysis of sequential effects with numeric stimuli

In a simulated absolute judgment task, subjects guessed which numeral would appear next in a random sequence. Feedback was given after every trial. The average response for the nth trial was analyzed as a joint function of both the response and the feedback for the previous trial. The results confirm those of an earlier study by Ward and Lockhead (1971). Two new models are proposed to explain sequence effects in this task of infinite difficulty. Although computer simulations based on the models fit the data reasonably well, problems remain when attempts are made to apply the same theoretical reasoning to absolute judgment tasks involving actual stimuli.     

A note on interobserver reliability for sequential data

It is well accepted that reliability measures based on simple frequency counts of designated codes are inappropriate for sequential analysis. The stricter point-by-point method, however, is problematic, particularly because it is too strict. It is suggested that a less strict reliability measure based on the number of transitions be used. This method also avoids problems encountered with the point-by-point method and another less stringent method.     

A note on the sequential probability ratio test

Link and Heath [1975] have analysed a random walk model for two-choice reaction time on the assumption that the two probability density functions (p.d.f.s) of the step-size, each p.d.f. corresponding to one stimulus, are mirror reflections of each other; and they have demonstrated the critical role played by the symmetry of the moment generating function (m.g.f.) of the step size in the determination of whether or not error and correct reaction times are equal. It is shown here that, given reflection symmetry, m.g.f. symmetry is necessary and sufficient for the random walk model to be equivalent to a sequential probability ratio test.