Minimal Memory Demands Research Articles

Periodic fluctuations in reading times reflect multi-word-chunking

Memory is fleeting. To avoid information loss, humans need to recode verbal stimuli into chunks of limited duration, each containing multiple words. Chunk duration may also be limited neurally by the wavelength of periodic brain activity, so-called neural oscillations. While both cognitive and neural constraints predict some degree of behavioral regularity in processing, this remains to be shown. Our analysis of self-paced reading data from 181 participants reveals periodic patterns at a frequency of sim 2 Hz. We defined multi-word chunks by using a computational formalization based on dependency annotations and part-of-speech tags. Potential chunk outputs were first generated from the computational formalization and the final chunk outputs were selected based on normalized pointwise mutual information. We show that behavioral periodicity is time-aligned to multi-word chunks, suggesting that the multi-word chunks generated from local dependency clusters may minimize memory demands. This is the first evidence that sentence processing behavior is periodic, consistent with a role of both memory constraints and endogenous electrophysiological rhythms in the formation of chunks during language comprehension.

Local Second-Order Møller-Plesset Theory with a Single Threshold Using Orthogonal Virtual Orbitals: Theory, Implementation, and Assessment.

It has long been clear that electron correlation methods exhibit unphysical compute scalings with molecular size, which has motivated the development of local correlation methods to discard effectively zero contributions in a controlled way to yield an approximate correlation energy. The ideal local correlation method should have a single numerical threshold that controls the dropping of terms with the ability to have that threshold set small enough so that the correlation energy is reproduced to enough significant figures such that the result is chemically identical. This work reports such a method for the second-order Møller-Plesset (MP2) theory. The theory, implementation, and testing of this local MP2 theory are reported. Thresholds ranging from 10-5 to 10-8 and basis sets ranging from split valence plus polarization through to quadruple-ζ are assessed for local MP2 calculations on a range of molecules, including linear chains and molecules with two- and three-dimensional character. The implementation is shared memory parallel via OpenMP and yields roughly 50% parallel efficiency with 16 cores for a large job. Considerable efforts were made to minimize memory demands, which increased as thresholds were tightened. A variety of relative energy calculations are presented as a function of threshold to provide some guidance to users on how to obtain adequate precision at a low compute cost. It is particularly clear that derivative properties require tighter thresholds in order to achieve an adequate precision.

Who is Right? A Word-Identification-in-Noise Test for Young Children Using Minimal Pair Distracters.

Many children have difficulties understanding speech. At present, there are few assessments that test for subtle impairments in speech perception with normative data from U.K. children. We present a new test that evaluates children's ability to identify target words in background noise by choosing between minimal pair alternatives that differ by a single articulatory phonetic feature. This task (a) is tailored to testing young children, but also readily applicable to adults; (b) has minimal memory demands; (c) adapts to the child's ability; and (d) does not require reading or verbal output. We tested 155 children and young adults aged from 5 to 25 years on this new test of single word perception. Speech-in-noise abilities in this particular task develop rapidly through childhood until they reach maturity at around 9 years of age. We make this test freely available and provide associated normative data. We hope that it will be useful to researchers and clinicians in the assessment of speech perception abilities in children who are hard of hearing or have developmental language disorder, dyslexia, or auditory processing disorder. https://doi.org/10.23641/asha.17155934.

Amount and delay insensitivity during intertemporal choice in three neurodegenerative diseases reflects dorsomedial prefrontal atrophy

Patients with Alzheimer's disease and other dementias often make poor financial decisions, but it remains unclear whether this reflects specific failures in decision-making or more general deficits in episodic and working memory. We investigated how patients with Alzheimer's disease, behavioral variant frontotemporal dementia (bvFTD), and semantic variant primary progressive aphasia (svPPA) apply information in an intertemporal choice task between smaller intermediate and larger delayed rewards, with minimal memory demands. Multilevel modeling estimated subject-level sensitivities to three attributes of choice (the relative difference in reward magnitude, delay length, and absolute reward magnitudes) as well as baseline impulsivity. While baseline impulsivity in patients with Alzheimer's disease did not differ from controls, patients with bvFTD and svPPA were more impulsive than controls overall. Patients with Alzheimer's disease or bvFTD were less sensitive than controls to all three choice attributes, whereas patients with svPPA were less sensitive than controls to two attributes. Attenuated sensitivity to information presented during the choice was associated across all subjects with dorsomedial prefrontal atrophy for all three choice attributes. Given the minimal memory demands of our task, these findings suggest specific mechanisms underlying decision-making failures beyond episodic and working memory deficits in dementia.

Evaluation of an Accessible, Real-Time, and Infrastructure-Free Indoor Navigation System by Users Who Are Blind in the Mall of America

Introduction: This article describes an evaluation of MagNav, a speech-based, infrastructure-free indoor navigation system. The research was conducted in the Mall of America, the largest shopping mall in the United States, to empirically investigate the impact of memory load on route-guidance performance. Method: Twelve participants who are blind and 12 age-matched sighted controls participated in the study. Comparisons are made for route-guidance performance between use of updated, real-time route instructions (system-aided condition) and a system-unaided (memory-based condition) where the same instructions were only provided in advance of route travel. The sighted controls (who navigated under typical visual perception but used the system for route guidance) represent a best case comparison benchmark with the blind participants who used the system. Results: Results across all three test measures provide compelling behavioral evidence that blind navigators receiving real-time verbal information from the MagNav system performed route travel faster (navigation time), more accurately (fewer errors in reaching the destination), and more confidently (fewer requests for bystander assistance) compared to conditions where the same route information was only available to them in advance of travel. In addition, no statistically reliable differences were observed for any measure in the system-aided conditions between the blind and sighted participants. Posttest survey results corroborate the empirical findings, further supporting the efficacy of the MagNav system. Discussion: This research provides compelling quantitative and qualitative evidence showing the utility of an infrastructure-free, low-memory demand navigation system for supporting route guidance through complex indoor environments and supports the theory that functionally equivalent navigation performance is possible when access to real-time environmental information is available, irrespective of visual status. Implications for designers and practitioners: Findings provide insight for the importance of developers of accessible navigation systems to employ interfaces that minimize memory demands.

Memory demands in linguistic compensation.

Individuals often modify speech characteristics to accommodate their listeners. In the present study, we investigate how speakers modify their speech in a dictation task and what this says about their beliefs with respect to the listener's information processing limitations. To do so, we asked participants to either read a set of numbers aloud, or dictate numbers so that another person could write them down. Our results suggest that speech modification in this task was not related to individual differences in working memory capacity, and could represent speakers' attempt to minimize working memory demands of the listener. This account is similar to minimal memory strategies, whereby individuals often try to minimize memory demands in cognitive tasks.

Mean square optimal NUFFT approximation for efficient non-Cartesian MRI reconstruction

The fast evaluation of the discrete Fourier transform of an image at non-uniform sampling locations is key to efficient iterative non-Cartesian MRI reconstruction algorithms. Current non-uniform fast Fourier transform (NUFFT) approximations rely on the interpolation of oversampled uniform Fourier samples. The main challenge is high memory demand due to oversampling, especially when multidimensional datasets are involved. The main focus of this work is to design an NUFFT algorithm with minimal memory demands. Specifically, we introduce an analytical expression for the expected mean square error in the NUFFT approximation based on our earlier work. We then introduce an iterative algorithm to design the interpolator and scale factors. Experimental comparisons show that the proposed optimized NUFFT scheme provides considerably lower approximation errors than the previous designs [1] that rely on worst case error metrics. The improved approximations are also seen to considerably reduce the errors and artifacts in non-Cartesian MRI reconstruction.

Memory, Perception, and the Medial Temporal Lobe: A Synthesis of Opinions

Memory, Perception, and the Medial Temporal Lobe: A Synthesis of Opinions

Strategies for Coping With Cognitive Impairments of Clients in Supported Employment

This study evaluated the strategies used by employment specialists to help clients in supported employment programs manage cognitive impairments that interfered with obtaining and keeping jobs. Twenty-five supported employment specialists were surveyed to identify strategies they used to help their clients cope with cognitive problems in the domains of attention, psychomotor speed, memory, and problem solving. Then, 50 employment specialists were surveyed to determine whether they used each of the different coping strategies generated in the first part of the study. For each strategy used, they rated how effective it was. Employment specialists reported using a total of 76 different strategies for helping their clients cope with cognitive difficulties. The specialists reported using an average of 48 different coping strategies, which they rated on average as just below effective. Strategies for dealing with attention problems were rated as more effective than strategies used in the other three domains. The number of coping strategies that they reported using was significantly correlated with the perceived effectiveness of the strategies and the proportion of clients in their caseload who were working. Supported employment specialists were actively involved in helping clients cope with their cognitive impairments. Use of more strategies was correlated with specialists' greater perceived effectiveness of the strategies and with higher rates of working clients on their caseloads, although the reasons for these associations are unclear. Further research is needed to evaluate whether employment specialists' use of more strategies to help clients cope with cognitive problems contributes to better work outcomes.

Strategies for Coping With Cognitive Impairments of Clients in Supported Employment

Strategies for Coping With Cognitive Impairments of Clients in Supported Employment

Predictors of Web Navigation Performance in a Life Span Sample of Adults

The influence of age, subject matter knowledge, working memory, reading abilities, spatial abilities, and processing speed on Web navigation was assessed in a sample of 41 participants between the ages of 19 and 83 years. Each participant navigated a stand-alone tourism Web site to find answers to 12 questions. Performance was measured using time per trial, number of pages per trial, and number of revisited pages per trial. Age did not influence the number of total pages or repeat pages visited, which were predicted by domain knowledge, working memory, and processing speed. Age was associated with slower times per trial, and the effect remained significant after controlling for working memory, processing speed, and spatial abilities. Only with the addition of subject matter knowledge and World Wide Web experience was the age effect eliminated. Actual or potential applications of this research include redesigning Web sites to minimize memory demands and enhance visual segmentation. The data also suggest that age differences in Web navigation can be offset partially by taking advantage of older adults' prior experiences in the domain.

Perceptual repetition blindness effects.

Repetition blindness (RB) may reveal a new limitation on human perceptual processing. Recently, however, researchers have attributed RB to postperceptual processes. The standard rapid serial visual presentation (RSVP) paradigm used in most RB studies is open to such objections. The "single-frame" paradigm introduced by J. C. Johnston and B. L. Hale (1984) allowed investigation of RB with minimal memory demands. Participants made a judgment about whether 1 masked target word was the same or different than a posttarget probe. Confidence ratings permitted use of signal detection methods. In the critical condition for RB, a precue of the posttarget word was provided prior to the target stimulus so that the required judgment amounted to whether the target did or did not repeat the precue word. In control treatments, the precue was an unrelated word or a dummy. Results showed that perceptual sensitivity was significantly reduced in the RB condition relative to baseline control conditions. The data showed that RB can be obtained under conditions in which memory problems are minimal and perceptual sensitivity is assessed independently of biases. RB therefore can be a perceptual phenomenon.

Alpha-2 adrenergic agonists decrease distractibility in aged monkeys performing the delayed response task.

With advancing age, monkeys become impaired on a test of spatial working memory, the delayed response task, and show increased susceptibility to interference from irrelevant stimuli (Bartus and Dean 1979). Alpha-2 adrenergic agonists such as clonidine and guanfacine have been shown to improve the delayed response performance of aged monkeys under standard testing conditions (e.g. Arnsten et al. 1988). The current study examined whether these drugs could protect the delayed response performance of aged monkeys when irrelevant stimuli were presented during the delay intervals. Aged monkeys were tested on the variable delayed response task with short delays to minimize memory demands and optimize performance on control (no interference) sessions. During interference sessions, distractors were presented during the delays on 9 of the 30 trials ("distractor" trials). If the aged monkeys had been pretreated with saline, performance was significantly disrupted by the irrelevant stimuli compared to matched saline control sessions. This impairment was not only evident on the 9 distractor trials, but on the 21 remaining "nondistractor" trials as well. However, if the aged monkeys had been pretreated with clonidine or guanfacine, performance was not impaired on the interference sessions. This beneficial effect of the alpha-2 agonists was most apparent on the nondistractor trials. Guanfacine was able to decrease the harmful effects of distraction without any apparent sedative side effects. Co-administration of the alpha-2 antagonists idazoxan or SKF104078 with clonidine blocked the protective effects of the agonist on delayed response performance, consistent with actions at alpha-2 adrenergic receptors. These findings suggest that alpha-2 agonists improve delayed response performance, at least in part, by helping to protect memory from irrelevant stimulation. Clonidine is already used in the treatment of Attention Deficit Disorder, and the current data suggest that guanfacine may also be useful in this regard.