109 research outputs found
Alpha-band Brain Dynamics and Temporal Processing: An Introduction to the Special Focus
No full textFor decades, the intriguing connection between the human alpha rhythm (an 8-to 13-Hz oscillation maximal over posterior cortex) and temporal processes in perception has furnished a rich landscape of proposals. The past decade, however, has seen a surge in interest in the topic, bringing new theoretical, analytic, and methodological developments alongside fresh controversies. This Special Focus on alpha-band dynamics and temporal processing provides an up-to-date snapshot of the playing field, with contributions from leading researchers in the field spanning original perspectives, new evidence, compre-hensive reviews and meta-analyses, as well as discussion of ongoing controversies and paths forward. We hope that the perspectives captured here will help catalyze future research and shape the pathways toward a theoretically grounded and mechanistic account of the link between alpha dynamics and temporal properties of perception
Alpha-Band Frequency and Temporal Windows in Perception: A Review and Living Meta-analysis of 27 Experiments (and Counting)
No full textTemporal windows in perception refer to windows of time within which distinct stimuli interact to influence perception. A simple example is two temporally proximal stimuli fusing into a single percept. It has long been hypothesized that the human alpha rhythm (an 8-to 13-Hz neural oscillation maximal over posterior cortex) is linked to temporal windows, with higher frequencies corresponding to shorter windows and finer-grained temporal resolution. This hypothesis has garnered support from studies demonstrating a correlation between individual differences in alpha-band frequency (IAF) and behavioral measures of temporal processing. However, nonsignificant effects have also been reported. Here, we review and meta-analyze 27 experiments correlating IAF with measures of visual and audiovisual temporal processing. Our results estimate the true correlation in the population to be between .39 and .53, a medium-to-large effect. The effect held when considering visual or audiovisual experiments separately, when examining different IAF estimation protocols (i.e., eyes open and eyes closed), and when using analysis choices that favor a null result. Our review shows that (1) effects have been internally and independently replicated, (2) several positive effects are based on larger sample sizes than the null effects, and (3) many reported null effects are actually in the direction predicted by the hypothesis. A free interactive web app was developed to allow users to replicate our meta-analysis and change or update the study selection at will, making this a “living” meta-analysis (randfxmeta.streamlit.app). We discuss possible factors underlying null reports, design recommendations, and open questions for future research
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From uncertainty to judgment: The neural footprint of metacognitive introspection in perceptual decisions
No full textDecision making is often accompanied by a subjective sense of confidence. This metacognitive evaluation of decision accuracy is critical for adaptive behavior, particularly in environments lacking external feedback. While confidence is linked to conscious perception and shapes behavioral adjustments, its integration into formal decision making models remains unresolved, and its neural mechanisms are poorly understood. Key questions persist: Does the sensory information driving confidence align with that underlying the initial choice? Does confidence evaluation alter decision dynamics? This dissertation addresses these gaps by investigating the computational and neurobiological basis of confidence in perceptual decision-making. Using motion stimuli, a central-parietal positive-going electroencephalogram component (CPP) behaves as an accumulating decision variable that predicts evidence quality, response time (RT), accuracy, and confidence. Additionally, the CPP was found to scale with confidence even when accuracy, RT, and evidence quality were controlled. This suggests that pre-decision CPP activity encodes subjective confidence, dissociable from objective performance metrics. Critically, the CPP slopes steepened during introspection (~250 ms post-evidence availability) when confidence was reported, but shallowed when confidence was held in mind without explicit reporting. These findings indicate that confidence modulates evidence accumulation dynamics, either amplifying or suppressing neural gain depending on task demands. Additionally, effector-specific motor signals emerged pre-decisionally, predicting subsequent confidence ratings even when confidence was not overtly reported. This demonstrates that confidence introspection alters neural evidence accumulation and recruits motor circuits in real-time, refuting models positing confidence as purely retrospective. Together, these results position confidence as a dynamic, action-oriented mechanism that recalibrates sensory and motor processing to optimize behavioral efficiency under uncertainty, aligning with frameworks where metacognition is temporally embedded in decision making
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The Speed of Sight: How Characteristics of Alpha Oscillations Relate to Rhythmic Sampling and Time Perception
No full textDespite a large body of research indicating that alpha oscillations are involved in visual processing, and particularly that alpha frequency relates to temporal resolution and discriminability of stimuli, the mechanisms underlying exactly how alpha shapes our conscious perception is still unclear. According to one account, perception could be discretely windowed by each alpha cycle into a series of “snapshots” (discrete sampling theory), while another account posits that just the strength of perception continuously waxes and wanes across each alpha cycle (rhythmic sampling theory). This dissertation examines features of alpha oscillations in the context of these theories of perceptual sampling. We demonstrate that perception is unlikely to occur in discrete snapshots, given that an individual’s alpha frequency (IAF) does not relate to the magnitude of their percepts across similar visual illusions that are thought to depend on discrete sampling, nor does it relate to the timing of sensory responses associated with visual percepts. Finally, we find that alpha does not relate to a bias in duration estimation, which should occur if individuals accumulate varying amounts of visual information via discrete perceptual snapshots due to their varying IAFs. However, we found support for the role of alpha oscillations in modulating the strength of our sensory percepts by demonstrating that alpha phase – and its interaction with alpha power – relates to the strength of sensory responses associated with visual perception, and that IAF relates to individual differences in sensitivity when estimating and discriminating the durations of visual events. These studies provide novel insights into how alpha oscillations play a role in visual processing, not just around the timing of a single alpha cycle, but also at longer durations of stimulus processing in a way that facilitates our perception of time
In vitro activity of antimicrobial agents against extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae at a tertiary care center in Lebanon
No full textLooking for therapeutic options, we assessed the minimum inhibitory concentrations (MICs) of 7 antimicrobial agents against extended-spectrum β-lactamase-producing Klebsiella pneumoniae (n = 58) and Escherichia coli (n = 84) isolates. High rates of susceptibility were shown for both E coli and K pneumoniae against ertapenem (100percent for both), piperacillin-tazobactam (83percent and 91percent, respectively) and amikacin (96percent and 82percent, respectively). In addition, most K pneumoniae isolates were susceptible to quinolones (72percent-75percent) and cefepime (88percent). However, clinical correlation is warranted. Copyright © 2005 by the Association for Professionals in Infection Control and Epidemiology, Inc.Araj G F, 2000, J Med Liban, V48, P221; Bradford PA, 2001, CLIN MICROBIOL REV, V14, P933, DOI 10.1128-CMR.14.4.933-951.2001; Iqbal M, 2002, J Pak Med Assoc, V52, P407; Jones LE, 1997, J ECON DYN CONTROL, V21, P1, DOI 10.1016-0165-1889(95)00924-8; KANAFANI ZA, 2004, 44 ICAAC OCT 29 NOV; Kanj S S, 2001, J Med Liban, V49, P13; Livermore DM, 2001, ANTIMICROB AGENTS CH, V45, P2831, DOI 10.1128-AAC.45.10.2831-2837.2001; National Committee for Clinical Laboratory Standards, 2002, M100S12 NAT COMM CLI; Nishino Takeshi, 2002, Nihon Rinsho, V60, P2216; Paterson DL, 2001, J CLIN MICROBIOL, V39, P2206, DOI 10.1128-JCM.39.6.2206-2212.2001; Samaha-Kfoury JN, 2003, BRIT MED J, V327, P1209, DOI 10.1136-bmj.327.7425.1209; Spanu T, 2002, ANTIMICROB AGENTS CH, V46, P196, DOI 10.1128-AAC.46.1.196-202.2002; Zanetti G, 2003, ANTIMICROB AGENTS CH, V47, P3442, DOI 10.1128-AAC.47.11.3442-3447.200396
Role of Hyoid Bone Position in Maintaining Upper Airway Patency
No full textJoseph G. Ghafari; Jason Amatoury; Anthony Macari; Hassan ChamiThe hyoid is a mobile bone located at the base of the tongue. It is the point of insertion for many of the muscles that control the geometry and mechanical properties of the upper airway (UA). Consequently, the hyoid is likely essential in maintaining upper airway patency, particularly when exposed to inspiratory negative pressures. Recurrent collapse of the upper airway during sleep is characteristic of obstructive sleep apnea (OSA), a highly prevalent respiratory sleep disorder with serious health risks. An inferiorly positioned hyoid is the most consistently observed anatomical difference between people with OSA and healthy controls. Surgical hyoid repositioning procedures are being performed to treat OSA patients, but outcomes are highly variable, primarily because of the lack of knowledge regarding the precise influence of hyoid position on upper airway function. The aim of this thesis is to determine the role of hyoid bone position in maintaining upper airway patency.
Seven anaesthetized, male, New Zealand White rabbits were tracheostomized and left to breath spontaneously via the caudal trachea (i.e. no UA airflow or muscle activity). The hyoid was repositioned within the mid-sagittal plane along cranial, caudal and anterior directions from baseline (0mm) to 5mm in 1mm increments, and along 30°, 45° and 60° cranial and caudal directions. These movement were performed using a custom-made device. The effect of hyoid position on upper airway patency was quantified using the upper airway closing pressure, Pclose (the negative pressure required to close the upper airway). On the basic premise that the more Pclose is negative, the less the upper airway is prone to collapse. Data were expressed as a change from baseline (0mm). Repeated measures ANOVA tests were performed to assess changes in key outcomes with hyoid displacement. Statistical significance was inferred for p <0.05.
The baseline Pclose before any hyoid repositioning was -3.55 ± 0.95 cmH2O (mean± SD). The anterior displacement of the hyoid resulted in the greatest decrease in Pclose amongst all directions (p=0.002). Pclose decreased progressively with each increment of anterior hyoid bone displacement, going down by 3.98 ± 1.31 cmH2O at 5mm. In contrast, when the hyoid was moved cranially or caudally, Pclose did not change from the initial baseline value (p= 0.723 and p=0.352 respectively). When the hyoid was moved in anterior-cranial 45° and anterior-caudal 45° directions, Pclose decreased significantly (p=0.001 and p=0.004 respectively) and at similar magnitudes to the anterior direction (p>0.05). Also, the anterior-cranial 60° and anterior-caudal 60° directions decreased Pclose by 3.81 ± 0.78 cmH2O and 4.29 ± 1.68 cmH2O respectively, which is similar to the improvement obtained with the anterior direction. The anterior-cranial 30° and anterior-caudal 30° improved Pclose to a lesser extent (2.22 ± 0.58 cmH2O and 2.73 ± 0.85 cmH2O respectively).
This is the first study to quantitatively examine the influence of hyoid bone position on upper airway patency. Study outcomes suggest that hyoid surgical interventions for OSA treatment and possibly mandibular advancement oral appliances should focus on increasing the amplitude of anterior hyoid repositioning as a main contributor to improved upper airway patency
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