Temporal Processing Tasks Research Articles

MMN and temporal processing in schizophrenia – the past, the present and the future

Aims/Background There is increasing evidence that individuals with schizophrenia exhibit impairments in the encoding of the temporal characteristics of sounds. The present study was designed to further explore this ability in individuals with schizophrenia in order to determine if impairment can be demonstrated on a range of temporal processing tasks: encoding of the duration (or length) or sounds, gap detection and interaural differences in timing (ITD).Conclusion This finding provides evidence for a pervasive impairment in the encoding of the temporal properties of sounds across a range of time scales in individuals with schizophrenia.

Temporal processing in poor adult readers

The aim of this study was to investigate the relationships between two different temporal processing tasks and word identification performance in skilled, dyslexic and poor adult readers. In Experiment 1 spatial and temporal sequencing tasks were conducted. It was found that adult dyslexics were significantly less accurate than skilled readers across all conditions in the temporal sequencing task, and when higher numbers of stimuli were presented in the spatial task. Experiment 2 replicated Experiment 1 in the temporal sequencing task and also found that poor readers had significantly higher motion coherence thresholds than those found in the skilled reader group. Ten percent of the variance in coherence thresholds was accounted for by performance on the temporal sequencing task. Multiple regression analyses determined that performance on the two temporal tasks could explain seventy percent of the variance in word identification scores, with the temporal sequencing task making the larger independent contribution. Experiment 3 replicated the findings of Experiment 2, while taking into account IQ, verbal memory and processing speed. Three things were concluded. First, the temporal tasks measure different aspects of temporal processing. The contribution to performance of higher-level perceptual and attentional components of the temporal sequencing task accounts for the relatively weak correlation found between the two measures. While sensory sensitivity to motion is measured at MT, the involvement of this area and PPC in higher-level perceptual and attentional processes is suggested by the findings of this study. Second, the association between temporal sequencing and reading skills may provide a stronger link between neural processing and poor reading skills than basic sensory processing measures alone, suggesting that a sensory magnocellular (M) system deficit cannot fully explain the relationship found between reading and visual neural processing. Third, problems with rapid sequential processing are predicted to be a generalised problem in poor adult readers, whether they are formally classified as dyslexic, or are poor performers on measures of word identification. Temporal processing may follow a distribution similar to that found for word identification skills.

Depression, attention, and time estimation

Depression is known to affect several cognitive functions, but little is known about the effect of this neuropsychological disorder on timing tasks. In the present experiment, 15 depressed and 20 non-depressed participants, classified on the basis of the Beck Depression Inventory, were tested on attentional and on temporal processing tasks. On the Continuous Performance Test, depressed participants made more omissions, but not more erroneous responses, than non-depressed participants. As well, discrimination of relatively long intervals (1120 vs 1280 ms) was poorer for the depressed group, which was not the case for discrimination of brief durations (80 vs 120 ms, and 450 vs 550 ms). Finally, there was a significant difference between groups regarding the variability of 1- or 10-s interval productions made with continuous series of finger taps. The attentional requirements of long-interval processing seems to be a critical factor in depression-induced deficits of temporal processing.

Neurons in the lateral agranular frontal cortex have divided attention correlates in a simultaneous temporal processing task.

The frontal cortex is an important brain area for divided attention. Lesions of the lateral agranular frontal cortex in rats disrupt divided attention in a simultaneous temporal processing task. In the present study, the activity of lateral agranular neurons was examined while rats performed a simultaneous temporal processing procedure. Rats were trained to time two stimuli (a light and a tone), each associated with a different fixed interval. Simple trials, in which a single stimulus was presented, and compound trials, in which both stimuli were presented simultaneously, occurred randomly in a session. Rats were able to divide attention between the two stimuli, as assessed by the pattern of lever presses. Approximately 50% of lateral agranular neurons responded to at least one phase of the task with four response patterns observed. The activity of type 1 cells (60%) was altered to compound, but not simple, stimuli. Type 2 cells (10%) responded to both types of simple stimuli and to compound stimuli. Type 3 cells (27%) had changes in firing rate to one type of simple stimulus and to compound stimuli. Type 4 cells (3%) responded to one type of simple stimulus, but were unresponsive to all other stimuli. The large proportion of type 1 cells supports the hypothesis that the lateral agranular cortex is important in divided attention. Previous studies have suggested that the lateral agranular cortex in rats is equivalent to the primary motor cortex. If so, the results from the present study provide evidence that the lateral agranular cortex may have some cognitive functions, in addition to being part of the motor system.

Cerebral correlates of working memory for temporal information.

Studies of neural correlates of working memory functions in the auditory-verbal, visuo-spatial and visuo-object domain suggest a category-specific organization of working memory processes in prefrontal cortex. Here, we used fMRI to explore brain areas that underlie different working memory operations directed to the temporal domain, which so far has been widely neglected. Significant activations related to memory updating and comparison processes were found right-accentuated in prefrontal and lateral premotor cortices. Furthermore, both subvocal rhythm encoding and maintenance enhanced left-lateralized activity in Broca's and supplementary motor area as well as in the sensorimotor cortex. Hemispheric lateralization effects of brain activity during temporal processing tasks may depend on the presence or absence of subvocal rehearsal strategies.

Temporal resolution and temporal masking properties of transient stimuli: data and an auditory model.

Temporal resolution is often measured using the detection of temporal gaps or signals in temporal gaps embedded in long-duration stimuli. In this study, psychoacoustical paradigms are developed for measuring the temporal encoding of transient stimuli. The stimuli consisted of very short pips which, in two experiments, contained a steady state portion. The carrier was high-pass filtered, dynamically compressed noise, refreshed for every stimulus presentation. The first experiment shows that, with these very short stimuli, gap detection thresholds are about the same as obtained in previous investigations. Experiments II and III show that, using the same stimuli, temporal-separation thresholds and duration-discrimination thresholds are better than gap-detection thresholds. Experiment IV investigates the significance of residual spectral cues for the listeners' performance. In experiment V, temporal separation thresholds were measured as a function of the signal-pip sensation level (SL) in both forward- and backward-masking conditions. The separation thresholds show a strong temporal asymmetry with good separation thresholds independent of signal-pip SL in backward-masking conditions and increasing separation thresholds with decreasing signal-pip SL in forward-masking conditions. A model of the auditory periphery is used to stimulate the gap-detection and temporal-separation thresholds quantitatively. By varying parameters like auditory-filter width and transduction time constants, the model provides some insight into how the peripheral auditory system may cope with temporal processing tasks and thus represents a more physiology-related complement to current models of temporal processing.

Effects of divided attention on temporal processing in patients with lesions of the cerebellum or frontal lobe.

Prefrontal cortex and cerebellum have both been implicated in temporal processing tasks although the exact contribution of each system remains unclear. To investigate this issue, control participants and patients with either prefrontal or cerebellar lesions were tested on temporal and nontemporal perceptual tasks under 2 levels of attentional load. Each trial involved a comparison between a standard tone and a subsequent comparison tone that varied in frequency, duration, or both. When participants had to make concurrent judgments on both dimensions, patients with frontal lobe lesions were significantly impaired on both tasks whereas the variability of cerebellar patients increased in the duration task only. This dissociation suggests that deficits on temporal processing tasks observed in frontal patients can be related to the attention demands of such tasks; cerebellar patients have a more specific problem related to timing.

Effects of divided attention on temporal processing in patients with lesions of the cerebellum or frontal lobe.

Prefrontal cortex and cerebellum have both been implicated in temporal processing tasks although the exact contribution of each system remains unclear. To investigate this issue, control participants and patients with either prefrontal or cerebellar lesions were tested on temporal and nontemporal perceptual tasks under 2 levels of attentional load. Each trial involved a comparison between a standard tone and a subsequent comparison tone that varied in frequency, duration, or both. When participants had to make concurrent judgments on both dimensions, patients with frontal lobe lesions were significantly impaired on both tasks whereas the variability of cerebellar patients increased in the duration task only. This dissociation suggests that deficits on temporal processing tasks observed in frontal patients can be related to the attention demands of such tasks; cerebellar patients have a more specific problem related to timing.

Evolutionary credit apportionment and its application to time-dependent neural processing

A new approach to training recurrent neural networks is applied to temporal neural processing problems. Our method combines Darwinian variation and selection with a credit apportionment mechanism for assigning credit to individual neurons within the groups of competing networks. Interconnections between the networks allow the outputs of neurons in one network to be available to the neurons in other networks. The firing behavior of the neurons in a variety of networks is compared with the corresponding neurons in high performing networks for specific input contexts. Payoffs accorded to neurons in one network can thus be shared with neurons in other networks. Only the best neurons over the entire repertoire of networks are allowed to pass their crucial function-determining parameters on to other neurons. The algorithm is demonstrated with connectionist-type units on several temporal processing tasks and compared to genetic algorithms.

Combining evolution with credit apportionment: A new learning algorithm for neural nets

A new approach is presented to Darwinian learning over a repertoire of competing neural nets that includes a credit apportionment algorithm for individual neurons within the networks. The architecture of the system is organized to allow the output of any given layer of a selected network to be available both to the next layer of this same network and also to the next layer of all of the other networks in the repertoire. The pathway through the selected network is considered the (temporarily) dominant pathway through the system architecture. This provides the basis for implementing a competition among single neurons across all of the networks. The firing behavior of the neurons in many networks is directly compared with the corresponding neurons in the dominant network. Payoffs accorded to neurons in one network can thus be shared with neurons in other networks. Neurons with the highest total payoffs will tend to be those that are most compatible with all of the network contexts associated with the best performance on any of the inputs. The algorithm is tested with connectionist-type units. Results include: successful learning experiments with temporal processing tasks using recurrent networks and several types of static learning tasks using analog input vectors. Performance comparisons are given with a standard genetic algorithm learning approach and, for the static learning problems, with standard back propagation as well.

Setting the Activity Level in Sparse Random Networks

We investigate the dynamics of a class of recurrent random networks with sparse, asymmetric excitatory connectivity and global shunting inhibition mediated by a single interneuron. Using probabilistic arguments and a hyperbolic tangent approximation to the gaussian, we develop a simple method for setting the average level of firing activity in these networks. We demonstrate through simulations that our technique works well and extends to networks with more complicated inhibitory schemes. We are interested primarily in the CA3 region of the mammalian hippocampus, and the random networks investigated here are seen as modeling the a priori dynamics of activity in this region. In the presence of external stimuli, a suitable synaptic modification rule could shape this dynamics to perform temporal information processing tasks such as sequence completion and prediction.

Auditory Temporal Acuity in Normally Achieving and Learning-Disabled College Students

Recent research has suggested that deficits in several metalinguistic/phonological abilities, such as short-term verbal memory and phoneme segmentation, may be etiologic factors in specific reading disability, and it has been speculated that these weaknesses may result from a more fundamental deficit in the processing of temporal, auditory stimuli. This study examined the auditory temporal processing skills of reading-disabled, math-disabled, and normally achieving college students. The math-disabled group was included to control for the possibility that poor temporal processing is a "marker" variable for learning disability rather than being related specifically to reading disability. Subjects were assessed on a battery of psychophysical tasks that included five tests of temporal processing. The reading-disabled group performed significantly more poorly on the temporal tasks but performed as well as the other groups on the simple pitch and loudness discrimination tasks. In spite of the significant difference on the temporal tasks, the majority of reading-disabled subjects performed within the same range as the subjects in the other two groups, and there were also some normally reading subjects who performed poorly on the temporal processing tasks. These findings suggest that poor temporal processing is neither a necessary nor a sufficient cause of reading disability, but that there is a modest association between the two domains.