The line-motion illusion can be reversed by motion signals after the line disappears

In the line-motion illusion, a briefly flashed line appears to propagate from the locus of attention, despite being physically presented on the screen all at once. It has been proposed that the illusion reflects low-level visual information processing that occurs faster at the locus of attention (Hikosaka et al 1993 Vision Research 33 1219-1240; Perception 22 517-526). Such an explanation implicitly embeds the assumption that speeding or slowing of neural signals will map directly onto perceptual timing. This 'online' hypothesis presupposes that signals which arrive first are perceived first. However, other evidence suggests that events in a window of time after the disappearance of a visual stimulus can influence the brain's interpretation of that stimulus (Eagleman and Sejnowski 2000 Science 287 2036-2038; 289 1107a; 290 1051a; 2002 Trends in Neuroscience 25 293). If the online hypothesis were true, we should expect that events occurring after the flashing of the line would not change the illusion. Consistent with our hypothesis that awareness is an a posteriori reconstruction, we demonstrate that the perceived direction of illusory line-motion can be reversed by manipulating stimuli after the line has disappeared.     

Preattentive perception of multiple illusory line-motion: a formal model of parallel independent-detection in visual search

The phenomenon referred to as illusory line-motion (ILM; O. Hikosaka, S. Miyauchi, & S. Shimojo, 1993a) has been described as a measure of the local facilitation of attention gradient. However, J. Kawahara, K. Yokosawa, S. Nishida, and T. Sato (1996) have demonstrated a spatially parallel search for an "odd man out" in the ILM direction. Apart from showing preattentive ILM perception in terms of an analogy between line-motion and apparent motion, the authors examined whether ILM perception is possible without attention from another point of view. Four experiments revealed that the ILM target can be detected in parallel without invoking attentional facilitation and invalidated the possible contribution of attentional set in parallel ILM search. Participants were able to correctly detect the ILM target among multiple nontargets, even when the line orientation was changed from trial to trial. The authors' independent-detection model predicted ILM search performance well on several occasions. These findings strongly support a preattentive and stimulus-driven explanation of ILM perception.     

Deprivation and reward stimuli as compound stimuli

In Experiment 1 the experimental group was tested with a deprivation level and a reward magnitude which it had experienced previously but which it had not experienced in combination. This group was inferior in test performance to a group which had experienced the test deprivation-reward combination prior to test. These results were interpreted as indicating that deprivation stimuli and reward stimuli form a compound stimulus and training on the elements of the compound produces performance inferior to training directly on the compound. In Experiment 2, the decrement associated with two different shifts in deprivation and reward did not differ despite the different size change of total incentive involved in the two shifts. The results were interpreted as indicating that the deprivation-reward stimulus is not produced by a single underlying incentive mechanism.     

Amplitude of constant-current pulses can be preset

The required magnitude of stimulation current can be adjusted with a voltage divider, consisting of a 10-turn potentiometer and a digital dial. This method of adjustment offers greater convenience than depending solely on a monitoring oscilloscope for current readings, especially when frequent changes in stimulation current must be made. Tissue polarization is prevented by a shunt gate, which is in operation during the pulse interval.     

Lateralization of two-transient stimuli

In this study of the precedence effect in binaural hearing, subjects adjusted the interaural delay of a wideband acoustic pointer to match the perceived intracranial position of transient test stimuli presented over headphones. The test stimuli had leading and lagging components (either brief noise bursts or clicks), each with its own interaural delay. In some test conditions, the leading and lagging stimuli were coherent copies of one another, whereas in others, they were independent samples of noise. The duration of the stimuli and the delay from the leading component to the lagging component were also varied. All the stimulus conditions showed a moderate or strong precedence effect (i.e., covariation of perceived lateral position of the composite two-transient stimulus with the interaural delay of the leading component). Predictions of the lateralization data are presented for variants of models based on temporal weighting and/or bandpass correlation. In one model variant, the binaural stimuli are temporally weighted to emphasize the onset and then subjected to bandpass correlation analysis. In another variant, it is assumed that the onset mechanism provides a rough estimate of the initial interaural delay that guides a slower and more focused bandpass correlation analysis. The accuracies of these two model's predictions were equivalent and superior to those of models that either represent leading and lagging cues equally (bandpass correlation with no onset effect) or do not represent lagging cues at all (a complete precedence effect). The results of these analyses show the need for both a strong onset effect and for bandpass correlation analysis and suggest two modeling approaches for achieving that goal.     

Compounding of pre-aversive stimuli

When two discriminative stimuli, each capable of maintaining a response, are combined, their compound will maintain a frequency of response greater than the frequencies maintained by the individual stimuli. This has been called additive summation. The present experiments extended the investigation of this phenomenon to a converse situation in which two pre-aversive stimuli were combined. Each pre-aversive stimulus was capable of reducing the frequency of an ongoing response. The combination of these stimuli reduced the relative frequency of response below that resulting from either stimulus. Furthermore, the compounding of two highly suppressive stimuli produced more suppression than the compounding of two less-suppressive stimuli. Evidence was also presented to suggest that the compound continued to reduce responding even when the single stimuli were no longer effective. A fourth experiment demonstrated that summation of response tendencies could not be accounted for in terms of stimulus intensity or sensory interaction.     

Forgetting trauma stimuli

Previous work reported in this journal suggested that the cognitive capacities of high dissociators are impaired under conditions of focused (selective) attention, but not under conditions of divided attention, compared with the cognitive capacities of low dissociators. Using a directed-forgetting paradigm, the current study demonstrated that under divided-attention demands, high dissociators have impaired memory for words associated with trauma (e.g., incest) but not for neutral words, as compared with low dissociators. In addition, high dissociators reported significantly more trauma history and significantly more betrayal trauma (abuse by a caregiver) than low dissociators. These results are consistent with the proposal that dissociation may aid individuals with histories of betrayal traumas to keep threatening information out of awareness.     

Creating noisy stimuli

A method for creating a variety of pseudo-random 'noisy' stimuli that possess several useful statistical and phenomenal features for psychophysical experimentation is outlined. These stimuli are derived from a pseudo-periodic function known as multidimensional noise. This class of function has the desirable property that it is periodic, defined on a fixed domain, is roughly symmetric, and is stochastic, yet consistent and repeatable. The stimuli that can be created from these functions have a controllable amount of complexity and self-similarity properties that are further useful when generating naturalistic looking objects and surfaces for investigation. The paper addresses the creation and manipulation of stimuli with the use of noise, including an overview of this particular implementation. Stimuli derived from these procedures have been used successfully in several shape and surface perception experiments and are presented here for use by others and further discussion as to their utility.     

Transfer of conditioned appetitive stimuli to conditioned aversive excitatory and inhibitory stimuli

The transfer of Pavlovian appetitive stimuli to Pavlovian aversive stimuli was examined in three experiments. In Experiment 1, rats received appetitive (Ap) conditioning designed to establish a flashing-light stimulus as either a CS+, CSo, or CS? for food, or to maintain it as a novel stimulus for US-alone subjects. Then, the stimulus was employed as a signal for weak shock in conditioned-emotional-response (CER) training. Both acquisition and extinction results showed that the ApCS+ facilitated and the ApCS? retarded aversive excitatory conditioning relative to the ApCSo and US-alone controls. Experiment 2 replicated the findings of Experiment 1 with both a moderate and a severe shock in CER training. In Experiment 3, different groups received the same appetitive conditioning as before, but to a flashing-light stimulus which was then employed as a signal for no shock in CER training. The ApCS? facilitated and the ApCS+ retarded aversive inhibitory conditioning relative to ApCSo and US-alone controls. Collectively, these findings establish that, in Pavlovian conditioning, transfer of an appetitive CS to an aversive excitor or inhibitor is facilitated by maintaining the initial conditioning contingency.     

Effects of rank ordering stimuli on magnitude ratings of these and other stimuli

Five experiments investigated the effects of rank ordering stimuli on subsequent magnitude ratings of these and other stimuli. In Experiments 1 and 2, subjects first rank ordered environmental issues in terms of their importance. Ranking stimuli from “most” to “least” led to more extreme ratings than ranking them from “least” to “most,” regardless of whether the rating criterion was the same as or diametrically opposite to the ranking criterion. (For example, subjects who had previously ranked them beginning with the most important issue subsequently rated these issues not only as more important, but also as more trivial, than did subjects who had ranked them beginning with the least important.) These effects generalized to stimuli other than those that had previously been ranked, and generalized over stimulus domains. (For example, ratings of environmental issues were also affected by ranking the importance of attributes of a marriage partner.) Other experiments in the series circumscribed the conditions in which these effects occur. Results suggested that rank ordering stimuli leads subjects to adopt comparative standards, the use of which generalizes to subsequent magnitude rating tasks and produces an anchoring bias similar to that identified by A. Tversky and D. Kahneman (1974, Science (Washington, D.C.), 185, 1124–1131). Implications of these results for the cognitive processes that underlie social judgment are discussed.     

Compounds of conditioned fear stimuli

A differential conditioning procedure was used with rats to establish different levels of suppression to two different stimuli. One stimulus was paired with shock every time it was presented, while the other stimulus cued shock on only 25% of its presentations. When these two component stimuli were subsequently tested as a simultaneous compound, two different types of component-compound relationships were observed. Some subjects showed greater suppression to the compound than they did to either component stimulus, while other subjects showed an intermediate level of suppression to the compound. The difference in type of component-compound relationship appeared to be related to the degree of stability (over trials) of each subject's reaction to the probabilistic (25%) cue.When a similar discrimination was established based on the intensity of the shock, rather than its probability of occurrence, all subjects showed more suppression to the compound than to its individual component stimuli. These results are discussed in terms of their implications for choice of model for characterizing the interaction of conditioned states.     

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.     

Categorical perception of stereoscopic stimuli

Two studies of the stereopsis model of Richards were conducted using a between-subjects balanced design and a repeated trials procedure rather than the within-subjects procedure of Richards. Measures of the accuracy of discrimination between classes of retinal disparity were defined by the method of successive intervals in place of the d’ index of SDT. The results support the predictions (1) of symmetric discrimination functions for convergent and divergent stimuli, (2) of greater discrimination for stimuli of 45 min of retinal disparity than for the stimuli of 15 min disparity, (3) of greater variability for the stimuli of greater disparity, and (4) of the use by nonanomalous subjects of at least two different processing mechanisms for stimuli of different disparity classes. The results do not support the prediction (1) of different processing mechanisms for foveal stimuli differing in figure-ground contrast or (2) of greater usefulness for monocular stimuli as a null disparity reference condition, as compared with binocular null disparity stimuli. Similar results were found for two stimulus shapes, a bar and a disk of equal area. Unreliability of subjects’ response systems was suggested as a factor in the prediction of figure-ground contrast changes and as a factor in the classification of subjects as stereo anomalous. The pattern of accuracy of discrimination between classes of disparity stimuli also raises questions of the adequacy of the simple stereopsis model.     

Digital generation of acoustic stimuli

A technique for digital generation of diverse acoustic waveforms is described. The method is embodied as a complete computer program coded in Fortran. We discuss the operation, implementation, and use of the program and its ease of adaptation for use on any computer.     

Minicomputer presentation of speech stimuli

A brief introduction to minicomputer control of speech stimuli is presented. Several techniques that have proven useful in this area are described.     

Function-altering effects of contingency-specifying stimuli

Contingengy-specifying stimuli (CSSs) can function differently than discriminative stimuli. Rather than evoking behavior due to a history of discrimination training, they alter the function of other stimuli and, therefore, the behavioral relations involving those stimuli. CSSs can alter the evocative function of discriminative stimuli, establishing operations, and conditional stimuli, as well as the efficacy of reinforcing and punishing stimuli and of stimuli that can function in second-order respondent conditioning. The concept of function-altering CSSs has implications for such areas of interest as stimulus equivalence, the terminology involving "rules" and "rule-governed behavior," and the way in which behavior analysts view the effects of such basic processes as reinforcement and punishment.     

Perception of two-component electrocutaneous stimuli

Electrocutaneous stimuli varying in strength (6, 8, 10 V) and frequency (9, 27, 81 Hzj were presented in pairs. Subjects were asked to give a numerical score to represent their perception of overall difference in a pair. To assess their ability to use numbers and their performance on unfamiliar stimuli, no guidance on the nature of the stimuli or the range or scale of the scores was given. Dimensional analysis indicated that perception of differences in one component was influenced by the absolute level of the other component, if this was constant in the pair, or by the difference. Considerable variation among subjects in the nature and extent of this interference effect was observed. Individual differences scaling (INDSCAL) enabled a satisfactory consensus model to be obtained. An empirical relationship expressing the observed twocomponent difference scores in terms of one-component scores was derived. Increasing voltage level diminished perception of frequency difference. Higher frequency levels augmented perception of voltage difference. This relationship is a modification of the combinatorial model proposed by Krantz and Tversky (1975). Individual differences in the combinatorial process are allowed for by application of the subject weightings from the INDSCAL solution.