Kimron L. Shapiro

Fragile visual short-term memory is an object-based and location-specific store

Fragile visual short-term memory (FM) is a recently discovered form of visual short-term memory. Evidence suggests that it provides rich and high-capacity storage, like iconic memory, yet it exists, without interference, almost as long as visual working memory. In the present study, we sought to unveil the functional underpinnings of this memory storage. We found that FM is only completely erased when the new visual scene appears at the same location and consists of the same objects as the to-be-recalled information. This result has two important implications: First, it shows that FM is an object- and location-specific store, and second, it suggests that FM might be used in everyday life when the presentation of visual information is appropriately designed.

Electrophysiological measurement of the effect of inter-stimulus competition on early cortical stages of human vision.

Competition between inputs in early visual cortex has been established as a key determinant in perception through decades of animal single cell and human fMRI research. We developed a novel ERP paradigm allowing this competition to be studied in humans, affording an opportunity to gain further insight into how competition is reflected at the neural level. Checkerboard stimuli were presented to elicit C1 (indexing processing in V1), C2 (hypothesized to reflect V1 after extrastriate feedback), and P1 (extrastriate) components. Stimuli were presented in three randomized conditions: single stimulus, near proximity pairs and far proximity pairs. Importantly, near stimuli (0.16° visual angle apart) were positioned to compete in primary visual cortex, whereas far stimuli (2° apart) were positioned to compete in extrastriate visual areas. As predicted, the degree and spatial range of competition increased from the C1 component to the C2 and P1 components. Specifically, competitive interactions in C1 amplitude were modest and present only for near-proximity pairs, whereas substantial competition was present for the P1, even for far-proximity pairs. To our knowledge, this is the first study to measure how competition unfolds over time in human visual cortex. Importantly, this method provides an empirical means of measuring competitive interactions at specific stages of visual processing, rendering it possible to rigorously test predictions about the effects of competition on perception, attention, and working memory.

Towards the Principled Study of Variable Autonomy in Mobile Robots

Safety critical and demanding tasks (e.g. Search and rescue or hazardous environments inspection), can benefit from robotic systems that offer a spectrum of control modes. These can range from direct teleoperation to full autonomy. This paper describes a pilot-study experiment in which a variable autonomy robot completes a navigation task. It explores the comparative performances of the human-robot system at different autonomy levels under different sets of conditions. This is done from a Mixed-Initiative system investigation perspective. Sensor noise was added to degrade robot performance, while a secondary task induced varying degrees of additional workload on the human operator. Carrying out these experiments and analyzing the initial results, has highlighted the profound complexities of designing tasks, conditions, and performance metrics which are: principled, eliminate confounding factors, and yield scientifically rigorous insights into the intricacies of a collaborative system that combines both human and robot intelligences. A key contribution of this paper is to describe the lessons learned from attempting these experiments, and to suggest a variety of guidelines for other researchers to consider when designing experiments in this context.

Alpha, Beta: The Rhythm of the Attentional Blink

Extant theories of the attentional blink propose that the most critical factor in determining second target accuracy is the time that elapses between the first and second targets. We report that this conclusion has overlooked an equally important determinant, namely, the frequency of the entraining stream in which these targets are embedded. Specifically, we show in two experiments that the signature of the attentional blink—second target accuracy that increases with intertarget lag—is significantly larger for entraining streams that are in the alpha-beta frequency range, relative to streams that are slower (theta) or faster (gamma). This finding ties the attentional blink critically, for the first time, to these two prominent oscillation frequencies that are known to be involved in the control of human attention and consciousness.

Experimental analysis of a variable autonomy framework for controlling a remotely operating mobile robot

This paper presents a principled experimental analysis of a variable autonomy control approach to mobile robot navigation. A Human-Initiative (HI) variable autonomy system is investigated, in which a human operator is able to switch the Level of Autonomy (LOA) between teleoperation (joystick control) and autonomous control (robot navigates autonomously towards waypoints selected by the human) on-the-fly. Our hypothesis is that the HI system will enable superior navigation performance compared to either teleoperation or autonomy alone, especially in scenarios where the performance of both the human and the robot may at times become degraded. We evaluate our hypothesis through carefully controlled and repeatable experiments using a significant number of human test-subjects.

Multisensory Integration: How Sound Alters Sight

What we hear can rapidly alter what we see. A new study provides evidence for a mechanism in which 10 Hz oscillations in the visual system define the time window for integrating auditory and visual information.

Spatiotemporal configuration of memory arrays as a component of VWM representations

Visual working memory (VWM) has been found to support a very limited representation of visual information and yet relatively little is known about the mechanisms that underlie this important cognitive construct. Prior investigations have revealed that VWM performance can be affected by relatively minor changes in the test method as well as the method of encoding. In the present two experiments, we separately investigated these two factors. The results suggest that sequential object displays can improve VWM performance significantly but that a lack of context relatedness between encoding and retrieval impairs performance. This impairment seems to be caused by a mismatch in the spatiotemporal configuration of the memory and test displays, and, importantly, cannot be compensated by selective attention. These findings suggest that spatiotemporal configuration information may be a fundamental component of the information that is stored in VWM as suggested by a number of influential theories.

EEG oscillations during word processing predict MCI conversion to Alzheimer's disease

Only a subset of mild cognitive impairment (MCI) patients progress to develop a form of dementia. A prominent feature of Alzheimers disease (AD) is a progressive decline in language. We investigated if subtle anomalies in EEG activity of MCI patients during a word comprehension task could provide insight into the likelihood of conversion to AD. We studied 25 amnestic MCI patients, a subset of whom developed AD within 3-years, and 11 elderly controls. In the task, auditory category descriptions (e.g., ‘a type of wood’) were followed by a single visual target word either semantically congruent (i.e., oak) or incongruent with the preceding category. We found that the MCI convertors group (i.e. patients that would go on to convert to AD in 3-years) had a diminished early posterior-parietal theta (3–5 Hz) activity induced by first presentation of the target word (i.e., access to lexico-syntactic properties of the word), compared to MCI non-convertors and controls. Moreover, MCI convertors exhibited oscillatory signatures for processing the semantically congruent words that were different from non-convertors and controls. MCI convertors thus showed basic anomalies for lexical and meaning processing. In addition, both MCI groups showed anomalous oscillatory signatures for the verbal learning/memory of repeated words: later alpha suppression (9–11 Hz), which followed first presentation of the target word, was attenuated for the second and third repetition in controls, but not in either MCI group. Our findings suggest that a subtle breakdown in the brain network subserving language comprehension can be foretelling of conversion to AD.

Competitive interactions affect working memory performance for both simultaneous and sequential stimulus presentation

Competition between simultaneously presented visual stimuli lengthens reaction time and reduces both the BOLD response and neural firing. In contrast, conditions of sequential presentation have been assumed to be free from competition. Here we manipulated the spatial proximity of stimuli (Near versus Far conditions) to examine the effects of simultaneous and sequential competition on different measures of working memory (WM) for colour. With simultaneous presentation, the measure of WM precision was significantly lower for Near items, and participants reported the colour of the wrong item more often. These effects were preserved when the second stimulus immediately followed the first, disappeared when they were separated by 500u2009ms, and were partly recovered (evident for our measure of mis-binding but not WM precision) when the task was altered to encourage participants to maintain the sequentially presented items together in WM. Our results show, for the first time, that competition affects the measure of WM precision, and challenge the assumption that sequential presentation removes competition.

Transcranial direct current stimulation can enhance working memory in Huntington's disease☆

ABSTRACT Transcranial direct current stimulation (tDCS) combined with a cognitive task can enhance targeted aspects of cognitive functioning in clinical populations. The movement disorder Huntingtons disease (HD) is associated with progressive cognitive impairment. Deficits in working memory (WM) can be apparent early in the disease and impact functional capacity. We investigated whether tDCS combined with cognitive training could improve WM in patients with HD, and if baseline clinical or cognitive measures may predict efficacy. Twenty participants with HD completed this crossover trial, undergoing 1.5 mA anodal tDCS over left dorsolateral prefrontal cortex and sham stimulation on separate visits. Participants and assessor were blinded to condition order, which was randomised across participants. All participants completed baseline clinical and cognitive assessments. Pre‐ and post‐stimulation tasks included digit reordering, computerised n‐back tests and a Stroop task. During 15 min of tDCS/sham stimulation, participants practiced 1‐ and 2‐back WM tasks. Participants exhibited an increase in WM span on the digit re‐ordering span task from pre‐ to post‐stimulation after tDCS, but not after sham stimulation. Gains in WM were positively related to motor symptom ratings and negatively associated with verbal fluency scores. Patients with more severe motor symptoms showed greatest improvement, suggesting that motor symptom ratings may help identify patients who are most likely to benefit from tDCS. Conclusions: Dorsolateral prefrontal tDCS appears well tolerated in HD and enhances WM span compared to sham stimulation. Our findings strongly encourage further investigation of the extent to which tDCS combined with cognitive training could enhance everyday function in HD. ClinicalTrials.gov; NCT02216474 Brain stimulation in Movement Disorders; https://clinicaltrials.gov/ct2/show/NCT02216474 HIGHLIGHTSTranscranial direct current stimulation may enhance working memory in HuntingtonsA double‐blind, sham‐controlled, crossover trial indicated good tolerabilityWM improved after dorsolateral prefrontal tDCS but not after sham stimulationEfficacy was related to baseline characteristics including motor symptom severity