Multimodal encoding in a simplified model of intracellular calcium signaling

Many cells use calcium signaling to carry information from the extracellular side of the plasma membrane to targets in their interior. Since virtually all cells employ a network of biochemical reactions for Ca²⁺ signaling, much effort has been devoted to understand the functional role of Ca²⁺ responses and to decipher how their complex dynamics is regulated by the biochemical network of Ca²⁺-related signal transduction pathways. Experimental observations show that Ca²⁺ signals in response to external stimuli encode information via frequency modulation (FM) or alternatively via amplitude modulation (AM). Although minimal models can capture separately both types of dynamics, they fail to exhibit different and more advanced encoding modes. By arguments of bifurcation theory, we propose instead that under some biophysical conditions more complex modes of information encoding can also be manifested by minimal models. We consider the minimal model of Li and Rinzel and show that information encoding can occur by AM of Ca²⁺ oscillations, by FM or by both modes (AFM). Our work is motivated by calcium signaling in astrocytes, the predominant type of cortical glial cells that is nowadays recognized to play a crucial role in the regulation of neuronal activity and information processing of the brain. We explain that our results can be crucial for a better understanding of synaptic information transfer. Furthermore, our results might also be important for better insight on other examples of physiological processes regulated by Ca²⁺ signaling.     

Multimodal encoding in a simplified model of intracellular calcium signaling

Many cells use calcium signaling to carry information from the extracellular side of the plasma membrane to targets in their interior. Since virtually all cells employ a network of biochemical reactions for Ca²⁺ signaling, much effort has been devoted to understand the functional role of Ca²⁺ responses and to decipher how their complex dynamics is regulated by the biochemical network of Ca²⁺-related signal transduction pathways. Experimental observations show that Ca²⁺ signals in response to external stimuli encode information via frequency modulation (FM) or alternatively via amplitude modulation (AM). Although minimal models can capture separately both types of dynamics, they fail to exhibit different and more advanced encoding modes. By arguments of bifurcation theory, we propose instead that under some biophysical conditions more complex modes of information encoding can also be manifested by minimal models. We consider the minimal model of Li and Rinzel and show that information encoding can occur by AM of Ca²⁺ oscillations, by FM or by both modes (AFM). Our work is motivated by calcium signaling in astrocytes, the predominant type of cortical glial cells that is nowadays recognized to play a crucial role in the regulation of neuronal activity and information processing of the brain. We explain that our results can be crucial for a better understanding of synaptic information transfer. Furthermore, our results might also be important for better insight on other examples of physiological processes regulated by Ca²⁺ signaling.     

Structure and strategy in image generation

Two experiments were conducted to test a prediction of the Kosslyn & Shwartz computer simulation model of mental image processing. According to this model, more complex images require more time to form because parts are placed sequentially, and larger images require more time to form than smaller ones because more parts are placed. If these accounts are correct, then the advantage of forming a small image (i.e., one that seems to subtend a smaller visual angle) should be greater for more complex objects because the difference in number of parts imaged at the two sizes will be greater than with simpler objects. This prediction was confirmed only when subjects were not motivated to form highly elaborated images at small sizes. When subject tried to include all details, it actually took longest to form images of complex objects at small sizes. Both of these results support the central assumption of the Kosslyn-Shwartz model, namely the existence of a fixed resolution analog spatial medium.     

The effects of emotion and encoding strategy on associative memory

Research has demonstrated that when discrete pieces of information are integrated together at encoding-imagining two items together as a single entity, for example-there is a mnemonic benefit for their relationship. A separate body of literature has indicated that the presence of emotional information can have an impact on the binding of associated neutral details, in some cases facilitating associative binding (MacKay et al. Memory and Cognition 32:474-488, 2004; Mather, Perspectives on Psychological Science 2:33-52, 2007), and in other cases impeding the processing of associated details (Easterbrook, Psychological Review 66:183-201, 1959; Kensinger, Emotion Review 1:99-113, 2009). In the present experiments, we investigated how memory for neutral words is affected by the emotionality of the information with which they are presented (whether with an emotional word or a second neutral word) and the encoding context (integrated or nonintegrated strategy). Participants viewed word pairs and were instructed to visualize the items as an integrated unit or to visualize them separately from one another. The results of Experiment 1 showed a disproportionate mnemonic benefit for neutral items that were integrated with other neutral items over those integrated with emotional items. The results of Experiments 2A and 2B showed that this effect interacted with encoding time: When given 2?s to encode, participants showed no effect of integration on memory for neutral-neutral pairs, but showed a significant mnemonic benefit for integrating emotional-neutral pairs. When given 4 or 6?s, the integrative benefit increased significantly for neutral-neutral pairs but decreased for emotional-neutral pairs. These results suggest that creating an integrated mental image of two neutral items requires a more time-consuming process than integrating an emotional and a neutral item, but that extra effort may result in a downstream mnemonic benefit.     

Effects of encoding strategy on long-term memory for odours

The effects of various encoding tasks on long-term recognition of odours were examined. Different groups of subjects were instructed (a) to form visual images of the source of the odour, (b) to generate the name of the odour and provide a dictionary-like definition, or (c) to describe a life episode of which the odour reminded them. A no-strategy control was simply told to try to remember the odours for a subsequent recognition test. One week later, subjects performed a yes-no recognition test for the odours. The second and third groups displayed significantly higher recognition than the controls. The visual imagery group did not differ significantly from the control group. The results seem to be accounted for best by dual coding theory.     

Structure and strategy in the associative false memory paradigm

List-learning experiments can have several levels of structure: individual words, the gist (if any) of each list, and the task in which those lists are embedded. The usual presentation of the DRM associative paradigm (Deese, 1959; Roediger & McDermott, 1995) strongly encourages a focus on gist and produces a high rate of false recall of key words (FRK). The experiments reported here were designed to invite the use of memory strategies based on structures other than the gist and thus reduce FRK. The crucial condition of Experiment 1, short lists followed by rehearsal, encouraged a focus on individual words and produced a low rate of FRK. In Experiment 2, the lists were embedded in a guessing game, which virtually eliminated FRK. FRK was also low in Experiments 3a and 3b when participants engaged in a complex task involving the first letters of list words. The relevance of these findings to false memories in the DRM and the connection of false autobiographical memories is discussed.     

Recognition memory as a function of encoding strategy and stimulus codability.

The primary purpose of this research was to determine how imaginal and verbal encoding strategies intereact with various stimulus characteristics to either enhance or retard recognition; the secondary purpose of these studies was to test the conceptual coding hypothesis of Ellis, 1972. A between-groups multivariate factorial analysis of covariance experiment and a within-subjects multivariate factorial analysis of variance experiment were conducted. In Experiment 1 it was found that low-codability shapes were better recognized under the verbal encoding set rather than the imaginal encoding verbal encoding sets; and high-codability shapes were not better recognized than low-codability shapes. However, in Experiment 2, where instructional set was a within-subjects factor, it was found that low-codability shapes were not better recognized under the verbal encoding set than the imaginal encoding set.     

Adaptive and qualitative changes in encoding strategy with experience: evidence from the test-expectancy paradigm

Three experiments demonstrated learners' abilities to adaptively and qualitatively accommodate their encoding strategies to the demands of an upcoming test. Stimuli were word pairs. In Experiment 1, test expectancy was induced for either cued recall (of targets given cues) or free recall (of targets only) across 4 study-test cycles of the same test format, followed by a final critical cycle featuring either the expected or the unexpected test format. For final tests of both cued and free recall, participants who had expected that test format outperformed those who had not. This disordinal interaction, supported by recognition and self-report data, demonstrated not mere differences in effort based on anticipated test difficulty, but rather qualitative and appropriate differences in encoding strategies based on expected task demands. Participants also came to appropriately modulate metacognitive monitoring (Experiment 2) and study-time allocation (Experiment 3) across study-test cycles. Item and associative recognition performance, as well as self-report data, revealed shifts in encoding strategies across trials; these results were used to characterize and evaluate the different strategies that participants employed for cued versus free recall and to assess the optimality of participants' metacognitive control of encoding strategies. Taken together, these data illustrate a sophisticated form of metacognitive control, in which learners qualitatively shift encoding strategies to match the demands of anticipated tests.     

Effects of encoding strategy,presentation modality,and scoring method on STM performance with the Peterson and Peterson technique

The Peterson and Peterson (1959) STM experiment was replicated with variation of presentation modality and encoding strategy. The effect of various scoring criteria was also analyzed. The recall data showed that a Peterson and Peterson type forgetting curve was obtained using auditory presentation and instructions to rehearse vocally the trigrams when scoring only completely correct recall within the first 3 sec of the recall interval. With visual presentation and instructions to find meaningful trigram interpretations, the forgetting curve was higher and much more flat, especially when scoring position correct recall within the total 0-10-sec recall interval. In a buildup of PI experiment, no buildup of PI could be detected when visual presentation was used together with instructions to find meaningful trigram interpretations. The importance of the different encoding activities for recall performance was discussed.     

Updating knowledge about encoding strategies: a componential analysis of learning about strategy effectiveness from task experience

Researchers have argued for age deficits in learning about the effects of encoding strategies from task experience, partly on the basis of absolute accuracy of metacognitive judgments. However, these findings could be attributed to factors other than age differences in learning. Forty older and 40 younger adults participated in 2 study-test trials in which they studied paired associates with imagery or repetition, predicted recall for the items, attempted recall, and postdicted recall. Recall was greater after imagery than repetition, yet this effect was not fully reflected by predictions made on Trial 1. Although both older and younger adults accurately postdicted recall from Trial 1, absolute accuracy of the predictions made on Trial 2 showed little improvement. By contrast, both age groups demonstrated increases in between-person correlations of predictions with recall, which is inconsistent with age deficits in knowledge updating. Thus, both older and younger adults had updated knowledge about the relative effects of the strategies, but such updating was not evident in the absolute accuracy of the predictions.     

Short-term recall by deaf signers of American Sign Language: implications of encoding strategy for order recall

Two experiments were conducted on short-term recall of printed English words by deaf signers of American Sign Language (ASL). Compared with hearing subjects, deaf subjects recalled significantly fewer words when ordered recall of words was required, but not when free recall was required. Deaf subjects tended to use a speech-based code in probed recall for order, and the greater the reliance on a speech-based code, the more accurate the recall. These results are consistent with the hypothesis that a speech-based code facilitates the retention of order information.     

Perceptual identification and encoding

Sequences containing 10 numbers from 1–20 were presented in serial-order or random-order at rates of 1/sec, 2/sec, and 4/sec for serial-order or same-orderrecall by eight Ss. Stimulus duration was constant, so that the interpresentation interval decreased as rate of presentation increased. Serial-order recall was greater for serial-order presentation than for random-order presentation. The decrease in recall as presentation rate increased was similar for both serial-order and random-order presentation. This result indicates that serial-order recall of random-order presentation does not involve reordering or repeated sequential scanning. It is consistent with the view that serial-order recall of serial-order presentation is greater because identification time is decreased. due to the decrease in the range of relevant alternatives, so that increased encoding time results in storage of more information.     

Circle graphs and monadic second-order logic

This article is part of a project consisting in expressing, whenever possible, graph properties and graph transformations in monadic second-order logic or in its extensions using modulo p cardinality set predicates or auxiliary linear orders. A circle graph is the intersection graph of a set of chords of a circle. Such a set is called a chord diagram. It can also be described by a word with two occurrences of each letter, called a double occurrence word. If a circle graph is prime for the split (or join) decomposition defined by Cunnigham, it has a unique representation by a chord diagram, and this diagram can be defined by monadic second-order formulas with the even cardinality set predicate. By using the (canonical) split decomposition of a circle graph, we define in monadic second-order logic with auxiliary linear orders all its chord diagrams. This construction uses the fact that the canonical split decomposition of a graph can be constructed in monadic second-order logic with help of an arbitrary linear order. We prove that the order of first occurrences of the letters in a double occurrence word w that represents a connected circle graph determines this word in a unique way. The word w can be defined by a monadic second-order formula from the word of first occurrences of letters. We also prove that a set of circle graphs has bounded clique-width if and only if all the associated chord diagrams have bounded tree-width.     

Perceptual interference at encoding enhances item-specific encoding and disrupts relational encoding: Evidence from multiple recall tests

Interfering with perception during encoding can enhance later memory, a phenomenon known as the perceptual interference effect. This effect is investigated in the context of the item-specific-relational framework (e.g., Hunt & McDaniel, 1993), which suggests that the perceptual interference enhances item-specific encoding and impedes relational encoding. Two experiments performed with multiple recall tests support this view. Prior research indicates that item-specific processing increases item gains across tests, whereas relational processing protects against item losses (e.g., Burns, 1993; Klein, Loftus, Kihlstrom, & Aseron, 1989). Consistent with the item-specific-relational framework, perceptual interference produced significant increases in both item gains and losses relative to a control condition.     

The difference between flipping strategy and spinning strategy in mental rotation

Murray (1997 Memory & Cognition 25 96-105) showed that, when an inverted object was mentally rotated to upright, the reaction time (RT) of flipping strategy (rotating in depth about the horizontal axis) was shorter than that of spinning strategy (rotating in the picture plane). We hypothesised the absence of representation at the intermediate position between the inverted and the upright representations in the flipping strategy, and investigated this hypothesis by a priming paradigm that included prime and probe tasks within one trial. In the prime task, participants were asked to mentally rotate an inverted object to upright. In the probe task, they were asked to judge whether two objects simultaneously presented were the same or different. The flipping strategy in the prime task did not prime the probe task, whereas the spinning strategy did. The present results suggest that there is no intermediate representation in the flipping strategy: the difference in RT between the flipping strategy and the spinning strategy may be attributed to whether there is an intermediate representation or not, which could explain why depth rotation is faster.     

Vocal cues in emotion encoding and decoding

This research examines the correspondence between theoretical predictions on vocal expression patterns in naturally occurring emotions (as based on the component process theory of emotion; Scherer, 1986) and empirical data on the acoustic characteristics of actors' portrayals. Two male and two female professional radio actors portrayed anger, sadness, joy, fear, and disgust based on realistic scenarios of emotion-eliciting events. A series of judgment studies was conducted to assess the degree to which judges are able to recognize the intended emotion expressions. Disgust was relatively poorly recognized; average recognition accuracy for the other emotions attained 62.8% across studies. A set of portrayals reaching a satisfactory level of recognition accuracy underwent digital acoustic analysis. The results for the acoustic parameters extracted from the speech signal show a number of significant differences between emotions, generally confirming the theoretical predictions.This research was supported by a grant from the Deutsche Forschungsgemeinschaft (Sche 156/8-5). The authors acknowledge collaboration of Westdeutscher Rundfunk, Cologne, in producing professional versions of actor emotion portrayals, and thank Kurt Balser, Theodor Gehm, Christoph Gierschner, Judy Hall, Ursula Hess, Alice Isen, and one anonymous reviewer for helpful comments and contributions.     

A simplified duality for implicative lattices and l-groups

A topological duality is presented for a wide class of lattice-ordered structures including lattice-ordered groups. In this new approach, which simplifies considerably previous results of the author, the dual space is obtained by endowing the Priestley space of the underlying lattice with two binary functions, linked by set-theoretical complement and acting as symmetrical partners. In the particular case of l-groups, one of these functions is the usual product of sets and the axiomatization of the dual space is given by very simple first-order sentences, saying essentially that both functions are associative and that the space is a residuated semigroup with respect to each of them.The author is supported at the Mathematical Institute of Oxford by a grant of the Argentinian Consejo de Investigations Cientificas y Tecnicas (CONICET). The author wishes to acknowledge the CONICET and the kind hospitality of the Mathematical Institute.