Interference in Immediate Spatial Memory: Shifts of Spatial Attention or Central executive Involvement?

Interference in serial spatial memory was investigated in six experiments. Experiment 1 replicated Experiment 2 by Smyth and Scholey (1994) in showing that listening to tones that originated from different directions interfered with spatial memory. Experiment 2 showed, however, that the effect of mere listening was not observed when this was the only interference condition experienced by the subject. In Experiment 3, a binary pitch discrimination task performed on spatially separated tones impaired recall performance to the same extent as did left-right decisions. The same disrupting effect was also observed when the tones were presented from the same direction in the pitch discrimination task (Experiment 4) as well as in a binary loudness discrimination task (Experiment 5). Finally, repeating heard words did not interfere, whereas a pitch discrimination performed on these same words disrupted recall (Experiment 6). It is argued that the disrupting effects reflect not a specifically spatial interference, but a central executive involvement in the rehearsal process in serial spatial memory.     

Reduced chromatic discrimination in children with autism spectrum disorders

Atypical perception in Autism Spectrum Disorders (ASD) is well documented ( Dakin & Frith, 2005 ). However, relatively little is known about colour perception in ASD. Less accurate performance on certain colour tasks has led some to argue that chromatic discrimination is reduced in ASD relative to typical development ( Franklin, Sowden, Burley, Notman & Alder, 2008 ). The current investigation assessed chromatic discrimination in children with high-functioning autism (HFA) and typically developing (TD) children matched on age and non-verbal cognitive ability, using the Farnsworth-Munsell 100 hue test (Experiment 1) and a threshold discrimination task (Experiment 2). In Experiment 1, more errors on the chromatic discrimination task were made by the HFA than the TD group. Comparison with test norms revealed that performance for the HFA group was at a similar level to typically developing children around 3 years younger. In Experiment 2, chromatic thresholds were elevated for the HFA group relative to the TD group. For both experiments, reduced chromatic discrimination in ASD was due to a general reduction in chromatic sensitivity rather than a specific difficulty with either red–green or blue–yellow subsystems of colour vision. The absence of group differences on control tasks ruled out an explanation in terms of general task ability rather than chromatic sensitivity. Theories to account for the reduction in chromatic discrimination in HFA are discussed, and findings are related to cortical models of perceptual processing in ASD.     

Dissociative patterns of foreperiod effects in temporal discrimination and reaction time tasks

This study examined whether the process of temporal preparation for a target stimulus is the same regardless of the task required by the target stimulus. To this end, the same variable-foreperiod design was used in a temporal discrimination task (Experiment 1) and a reaction time task (Experiment 2). In Experiment 1, both temporal sensitivity and perceived duration increased as a function of foreperiod, whereas in Experiment 2, foreperiod did not influence reaction time. Furthermore, both temporal sensitivity and perceived duration revealed an asymmetric sequential effect of foreperiod, but the pattern of this effect was opposite to the pattern observed in the reaction time task. Together these dissociative patterns of foreperiod effects suggest that the mechanism of temporal preparation depends on the task required by the target stimulus.     

Dissociative patterns of foreperiod effects in temporal discrimination and reaction time tasks

This study examined whether the process of temporal preparation for a target stimulus is the same regardless of the task required by the target stimulus. To this end, the same variable-foreperiod design was used in a temporal discrimination task (Experiment 1) and a reaction time task (Experiment 2). In Experiment 1, both temporal sensitivity and perceived duration increased as a function of foreperiod, whereas in Experiment 2, foreperiod did not influence reaction time. Furthermore, both temporal sensitivity and perceived duration revealed an asymmetric sequential effect of foreperiod, but the pattern of this effect was opposite to the pattern observed in the reaction time task. Together these dissociative patterns of foreperiod effects suggest that the mechanism of temporal preparation depends on the task required by the target stimulus.     

Effects of an auditory model on the learning of relative and absolute timing

The effects of an auditory model on the learning of relative and absolute timing were examined. In 2 experiments, participants attempted to learn to produce a 1,000- or 1,600-ms sequence of 5 key presses with a specific relative-timing pattern. In each experiment, participants were, or were not, provided an auditory model that consisted of a series of tones that were temporally spaced according to the criterion relative-timing pattern. In Experiment 1, participants (n = 14) given the auditory template exhibited better relative- and absolute-timing performance than participants (n = 14) not given the auditory template. In Experiment 2, auditory and no-auditory template groups again were tested, but in that experiment each physical practice participant (n = 16) was paired during acquisition with an observer (n = 16). The observer was privy to all instructions as well as auditory and visual information that was provided the physical practice participant. The results replicated the results of Experiment 1: Relative-timing information was enhanced by the auditory template for both the physical and observation practice participants. Absolute timing was improved only when the auditory model was coupled with physical practice. Consistent with the proposal of D. M. Scully and K. M. Newell (1985), modeled timing information in physical and observational practice benefited the learning of the relative-timing features of the task, but physical practice was required to enhance absolute timing.     

Effects of practice and signal energy on duration discrimination of brief auditory intervals

In Experiment 1, the proposition that duration discrimination of filled auditory intervals is based on temporal information rather than on energy-dependent cues was tested in 64 naive subjects. The subjects were presented with two auditory stimuli at different levels of intensity within one trial, and had to decide which of the two was longer in duration. An adaptive psychophysical procedure was used. As a measure of performance, difference threshold estimates in relation to a 50-msec standard interval were computed. Duration discrimination showed no effect of energy values, indicating that the subjects’ discrimination was independent of stimulus intensity. The goal of Experiments 2A and 2B was to investigate the effects of practice on duration discrimination which, in addition, may provide an indirect test for the potential use of energy-dependent cues. Effects of practice on duration discrimination of filled (Experiment 2 A) and empty (Experiment 2B) intervals were studied in 6 subjects in each case, over 20 testing sessions. An adaptive psychophysical procedure that was similar to the one used in Experiment 1 was applied. Neither short-term effects of practice based on the first five testing sessions, nor long-term effects of practice based on the means of 4 consecutive weeks, could be demonstrated. The results of the present study suggest that duration discrimination of brief auditory intervals is based on temporal information and not on stimulus energy. Furthermore, implications for the notion of a very basic bio-logical timing mechanism underlying temporal processing of brief auditory intervals in the range of milliseconds are discussed.     

Causal Induction in the Presence of a Perfect Negative Cue: Contrasting Predictions from Associative and Statistical Models

Two experiments on human causal induction with multiple candidate causes are reported. Experiment 1 investigated the influence of a perfect preventive cause on the ratings of a less contingent cause. Whereas the Rescorla-Wagner model (RWM) and Cheng's probabilistic contrast model predict that the less contingent cause should be completely discounted, the Pearce model predicts, in most cases, an enhancement of that cause's perceived importance. Results corresponded more closely tothe predictions of the Pearce model.The predictions of both the RWM and the Pearce model rely on a constant context cue acquiring associative strength, yet no such cue was explicitly identified in the task scenario employed in Experiment 1. Experiment 2 replicated a number of key conditions of Experiment 1 with a task scenario that afforded ratings of the causal importance of the context in which the effectiveness of the discrete candidate causes was evaluated. In addition, the number of trials was increased to test the possibility that the ratings in Experiment 1 were the product of incomplete learning. The results of the first experiment were replicated and the ratings of the effectiveness of the context cue were anticipated by both the RWM and the Pearce model. Overall, the Pearce model offers a more comprehensive account of the causal inferences recorded in this study.     

Practice-related reduction of dual-task costs under conditions of a manual-pedal response combination

Severe dual-task costs emerge when two tasks are performed at the same time. Schumacher, Seymour, Glass, Kieras, and Meyer (2001) showed a complete reduction of dual-task costs after extensive dual-task practice with a visual-manual (VM) task and an auditory-verbal (AV) task. First, we replicated these findings and found task conditions sufficient to achieve a high level of dual-task cost reduction (Experiment 1). Using these conditions, we tested whether the Schumacher et al. findings generalise to a different dual-task situation, in which participants practised a VM task and an auditory-pedal (AP) task (VM-AP) conjointly (Experiment 2). In the VM-AP task situation we found reduced dual-task costs after practice. Dual-task costs, however, remained on a high level after eight sessions of practice and also when extending practice to 12 sessions. No single participant showed evidence for time sharing in the VM-AP dual task. These results suggest that the finding of complete dual-task cost reduction does not generalise to the VM-AP task combination used in the present study. We discuss different factors potentially relevant for the observation of persisting dual-task costs over practice in the VM-AP task.     

Paradoxical Sleep Deprivation and Sleep Recording Following Training in a Brightness Discrimination Avoidance Task in Sprague–Dawley Rats: Paradoxical Effects

Previously, we reported that posttraining paradoxical sleep deprivation (PSD) resulted in an enhancement of the subsequent avoidance performance for rats trained for 15 trials in a Y-maze brightness avoidance discrimination task. A series of experiments were conducted to try to further understand the reasons for results which were contrary to those of the bulk of the sleep-learning literature. Experiment 1 investigated the effectiveness of the PSD technique. Rats (N= 4) were sleep recorded while residing on a “swimming pool” apparatus for 24 h. Compared to their baseline values, all animals showed a very large reduction in paradoxical sleep and spent significantly more time awake. Slow-wave sleep was unchanged. In Experiment 2, proactive motor effects were tested. Rats were deprived of PS for 24 h and then tested in a hole board motor activity task. There was a slight effect of PS deprivation on the day following the PSD and no effect when the rats were retested 1 week later. Experiment 3 investigated possible proactive effects of PSD on avoidance performance. Rats exposed to PSD in the 24 h before training in the Y-maze task did not demonstrate any facilitative effect on the subsequent avoidance performance. Experiment 4 investigated the possibility that the PSD facilitative effect could be due to partial training. Rats were given 75 acquisition trials in the brightness discrimination Y-maze avoidance before being subjected to 24 h of PSD. PS-deprived animals showed superior avoidance scores compared to non-PSD controls when retested 24 h later. In Experiment 5, the same strain of rats (N= 11) were sleep recorded after exposure to a partial acquisition in a Y-maze brightness avoidance discrimination task. They were then continuously monitored for 4 consecutive days. The percent PS for the Trained rats was significantly lower than that for the Control animals. This drop in percent PS was not confined to any particular time period in the 24-h day. None of the other sleep parameters reached significance. Analyses of the present results suggest that PSD exerts its facilitative effects on posttraining consolidation processes. We present arguments suggesting that PSD can have effects opposite to those generally reported, in animals demonstrating poor avoidance abilities, in an avoidance task.     

What happens to an individual visual working memory representation when it is interrupted?

This study tested the hypothesis that even the simplest cognitive tasks require the storage of information in working memory (WM), distorting any information that was previously stored in WM. Experiment 1 tested this hypothesis by requiring observers to perform a simple letter discrimination task while they were holding a single orientation in WM. We predicted that performing the task on the interposed letter stimulus would cause the orientation memory to become less precise and more categorical compared to when the letter was absent or when it was present but could be ignored. This prediction was confirmed. Experiment 2 tested the modality specificity of this effect by replacing the visual letter discrimination task with an auditory pitch discrimination task. Unlike the interposed visual stimulus, the interposed auditory stimulus produced little or no disruption of WM, consistent with the use of modality‐specific representations. Thus, performing a simple visual discrimination task, but not a simple auditory discrimination task, distorts information about a single feature being maintained in visual WM. We suggest that the interposed task eliminates information stored within the focus of attention, leaving behind a WM representation outside the focus of attention that is relatively imprecise and categorical.     

Discrimination of structure: I. Implications for connectionist theories of discrimination learning

In each of 4 experiments animals were given a structural discrimination task that involved visual patterns composed of identical features, but the spatial relations among the features were different for reinforced and nonreinforced trials. In Experiment 1 the stimuli were pairs of colored circles, and pigeons were required to discriminate between patterns that were the mirror image of each other. A related task was given to rats in Experiment 2. Subjects solved these discriminations. For Experiment 3, some pigeons were given a discrimination similar to that used in Experiment 1, which they solved, whereas others received a comparable task but with 3 colored circles present on every trial, which they failed to solve. The findings from Experiment 3 were replicated in Experiment 4 using different patterns. The results are difficult to explain by certain connectionist theories of discrimination learning, unless they are modified to take account of the way in which compound stimuli are structured.     

Effects of an Auditory Model on the Learning of Relative and Absolute Timing

The effects of an auditory model on the learning of relative and absolute timing were examined. In 2 experiments, participants attempted to learn to produce a 1,000- or 1,600-ms sequence of 5 key presses with a specific relative-timing pattern. In each experiment, participants were, or were not, provided an auditory model that consisted of a series of tones that were temporally spaced according to the criterion relative-timing pattern. In Experiment 1, participants (n = 14) given the auditory template exhibited better relative- and absolute-timing performance than participants (n = 14) not given the auditory template. In Experiment 2, auditory and no-auditory template groups again were tested, but in that experiment each physical practice participant (n = 16) was paired during acquisition with an observer (n = 16). The observer was privy to all instructions as well as auditory and visual information that was provided the physical practice participant. The results replicated the results of Experiment 1: Relative-timing information was enhanced by the auditory template for both the physical and observation practice participants. Absolute timing was improved only when the auditory model was coupled with physical practice. Consistent with the proposal of D. M. Scully and K. M. Newell (1985), modeled timing information in physical and observational practice benefited the learning of the relative-timing features of the task, but physical practice was required to enhance absolute timing.     

Is color “categorical perception” really perceptual?

Roberson and Davidoff (2000) found that color categorical perception (CP; better cross-category than within-category discrimination) was eliminated by verbal, but not by visual, interference presented during the interstimulus interval (ISI) of a discrimination task. On the basis of this finding, Roberson and Davidoff concluded that CP was mediated by verbal labels, and not by perceptual mechanisms, as is generally assumed. Experiment 1 replicated their results. However, it was found that if the interference type was uncertain on each trial (Experiment 2), CP then survived verbal interference. Moreover, it was found that the target color name could be retained across the ISI even with verbal interference (Experiment 3). We therefore conclude that color CP may indeed involve verbal labeling but that verbal interference does not necessarily prevent it.     

An analysis of emergent simple discrimination in children

In Experiment 1 eight five-year-old children received an arbitrary matching-to-sample task with sample stimuli A1 and A2 and comparison stimuli B1 and B2. This task was mixed with a simple, two-choice discrimination task with stimuli A1 and A2. In subsequent tests with B1 and B2 presented alone, the number of responses to B1 was greater when it had been paired with the correct stimulus of the simple discrimination task than when it had been paired with the incorrect stimulus. In Experiment 2 incorrect comparisons were omitted during the matching-to-sample task. Eight children were taught to point to either A1 or A2 first, and to either B1 or B2 second. Eight other children were taught to point to either B1 or B2 first, and to either A1 or A2 second. The effect of Experiment 1 was replicated with the first but not with the second group. The results of both experiments suggest that the functions of S+ and S- in a simple discrimination task can transfer to test stimuli if the training stimuli precede the test stimuli during paired presentations.     

Interlimb coordination: Learning and transfer under different feedback conditions

The role of intrinsic and extrinsic information feedback in learning a new bimanual coordination pattern was investigated. The pattern required continuous flexion-extension movements of the upper limbs with a 90 ° phase offset. Separate groups practiced the task under one of the following visual feedback conditions: (a) blindfolded (reduced FB group), (b) with normal vision (normal FB group), or (c) with concurrent relative motion information (enhanced FB group). All groups were subjected to three different transfer test conditions at regular intervals during practice. These tests included reduced, normal vision, and enhanced vision conditions. Experiment 1 showed that the group receiving augmented information feedback about its relative motions in real-time produced the required coordination pattern more successfully than the remaining two groups, irrespective of the transfer conditions under which performance was evaluated. Experiment 2 replicated and extended the superiority of the enhanced feedback group during acquisition and retention. Experiment 3 demonstrated that successful transfer to various transfer test conditions was not a result of test-trial effects. Overall, the data suggest that the conditions that optimized performance of the coordination pattern during acquisition also optimized transfer performance.     

Involuntary covert orienting is contingent on attentional control settings.

Four experiments tested a new hypothesis that involuntary attention shifts are contingent on the relationship between the properties of the eliciting event and the properties required for task performance. In a variant of the spatial cuing paradigm, the relation between cue property and the property useful in locating the target was systematically manipulated. In Experiment 1, invalid abrupt-onset precues produced costs for targets characterized by an abrupt onset but not for targets characterized by a discontinuity in color. In Experiment 2, invalid color precues produced greater costs for color targets than for abrupt-onset targets. Experiment 3 provided converging evidence for this pattern. Experiment 4 investigated the boundary conditions and time course for attention shifts elicited by color discontinuities. The results of these experiments suggest that attention capture is contingent on attentional control settings induced by task demands.     

Stimulus-specific processing consequences of pattern goodness

Two issues concerning the effects of visual pattern goodness on information processing time were investigated: the role of memory vs. encoding and the role of individual stimulus goodness vs. stimulus similarity. A sequential “same-different” task was used to provide differentiation of target item or memory effects from display item or encoding effects. Experiment 1 used four alternative stimuli in each block of trials. The results showed that good patterns were processed faster than poor patterns for both “same” and “different” responses. Furthermore, the goodness of the target item had a greater effect on reaction time than did the goodness of the display item, indicating that memory is more important than encoding in producing faster processing of good stimuli. Effects of interstimulus similarity on processing time were minimal, although isolation of good stimuli in a similarity space could explain many of the results. Experiment 2 replicated the results of Experiment 1, despite the fact that differences in similarity space had been minimized by using only two alternative stimuli in each block. In addition, the speed of processing a “same” pair was essentially independent of the particular alternative stimulus in a block. These results suggest that in this task, there is a processing advantage for good stimuli that is stimulus specific, with the effect operating primarily in memory.     

Surface features can deeply affect artificial grammar learning

Three experiments explored the extent to which surface features explain discrimination between grammatical and non-grammatical strings in artificial grammar learning (AGL). Experiment 1 replicated Knowlton and Squire’s (1996) paradigm using either letter strings as in the original study, or an analogous set of color strings to further explore if learning was affected by type of stimuli. Learning arose only with letter strings, but the results were mostly due to the discrimination of non-grammatical strings containing highly salient illegal features. Experiments 2 and 3 tested a new grammar devised to control for those features. Experiment 2 showed reduced grammar learning effects, and again only for letter materials. Experiment 3 explored the effect of additional practice with letter stimuli, and found increased learning only in the spaced practice condition, though additional practice also produced more explicit knowledge. These findings call for further research on the boundary conditions of learning in AGL paradigms.     

Applying the attractor field model to social cognition: Perceptual discrimination is facilitated, but memory is impaired for faces displaying evaluatively congruent expressions

A new model of mental representation is applied to social cognition: the attractor field model. Using the model, the authors predicted and found a perceptual advantage but a memory disadvantage for faces displaying evaluatively congruent expressions. In Experiment 1, participants completed a same/different perceptual discrimination task involving morphed pairs of angry-to-happy Black and White faces. Pairs of faces displaying evaluatively incongruent expressions (i.e., happy Black, angry White) were more likely to be labeled as similar and were less likely to be accurately discriminated from one another than faces displaying evaluatively congruent expressions (i.e., angry Black, happy White). Experiment 2 replicated this finding and showed that objective discriminability of stimuli moderated the impact of attractor field effects on perceptual discrimination accuracy. In Experiment 3, participants completed a recognition task for angry and happy Black and White faces. Consistent with the attractor field model, memory accuracy was better for faces displaying evaluatively incongruent expressions. Theoretical and practical implications of these findings are discussed.     

Vibrotactile pattern isolation/integration

Temporal integration has been cited as a major factor in temporal masking. Two experiments were designed to examine the conditions under which temporal integration may aid or hinder the perception of vibrotactile spatial patterns. In Experiment 1, the subject’s task was to discriminate between pairs of patterns. Each pattern was composed of two temporally separated pattern elements. When the task required the subjects to perceive the individual pattern elements, performance improved with temporal isolation—that is, performance improved as the temporal separation between the elements increased. In a second task, when the discrimination could be based on either the overall pattern shape or the pattern elements, temporal integration appeared to improve performance—that is, performance improved as the temporal separation decreased. In Experiment 2, an identification task was used. Several factors appeared to determine whether temporal integration aided or hindered pattern identification. When pattern elements similar to those in Experiment 1 were tested, performance improved with increasing temporal separation (isolation). A single function was fit to the discrimination (isolation) and identification (isolation) results. Whether temporal integration aids or hinders pattern perception appears to depend on pattern shape, the pattern elements, and the nature of the task.