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Todd J.,University of Newcastle | Todd J.,Schizophrenia Research Institute | Heathcote A.,University of Newcastle | Mullens D.,University of Newcastle | And 4 more authors.
Brain Topography | Year: 2014

Repetitious patterns enable the auditory system to form prediction models specifying the most likely characteristics of subsequent sounds. Pattern deviations elicit mismatch negativity (MMN), the amplitude of which is modulated by the size of the deviation and confidence in the model. Todd et al. (Neuropsychologia 49:3399-3405, 2011; J Neurophysiol 109:99-105, 2013) demonstrated that a multi-timescale sequence reveals a bias that profoundly distorts the impact of local sound statistics on the MMN amplitude. Two sounds alternate roles as repetitious "standard" and rare "deviant" rapidly (every 0.8 min) or slowly (every 2.4 min). The bias manifests as larger MMN to the sound first encountered as deviant in slow compared to fast changing sequences, but no difference for the sound first encountered as a standard. We propose that the bias is due to how Bayesian priors shape filters of sound relevance. By examining the time-course of change in MMN amplitude we show that the bias manifests immediately after roles change but rapidly disappears thereafter. The bias was reflected in the response to deviant sounds only (not in response to standards), consistent with precision estimates extracted from second order patterns modulating gain differentially for the two sounds. Evoked responses to deviants suggest that pattern extraction and reactivation of priors can operate over tens of minutes or longer. Both MMN and deviant responses establish that: (1) priors are defined by the most proximally encountered probability distribution when one exists but; (2) when no prior exists, one is instantiated by sequence onset characteristics; and (3) priors require context interruption to be updated. © 2013 Springer Science+Business Media. Source

Mullens D.,University of Newcastle | Woodley J.,University of Newcastle | Whitson L.,University of Newcastle | Provost A.,University of Newcastle | And 5 more authors.
Psychophysiology | Year: 2014

The role in which two tones are first encountered in an unattended oddball sequence affects how deviance detection, reflected by mismatch negativity, treats them later when the roles reverse: a "primacy bias." We tested whether this effect is modulated by previous behavioral relevance assigned to the two tones. To this end, sequences in which the roles of the two tones alternated were preceded by a go/no-go task in which tones were presented with equal probability. Half of the participants were asked to respond to the short sounds, the other half to long sounds. Primacy bias was initially abolished but returned dependent upon the go-stimulus that the participant was assigned. Results demonstrate a long-term impact of prior learning on deviance detection, and that even when prior importance/equivalence is learned, the bias ultimately returns. Results are discussed in terms of persistent go-stimulus specific changes in responsiveness to sound. © 2014 Society for Psychophysiological Research. Source

Pongracz A.,Institute for Technical Physics and Material Science | Fekete Z.,Institute for Technical Physics and Material Science | Marton G.,Institute for Technical Physics and Material Science | Marton G.,Institute of Cognitive Neuroscience and Psychology | And 5 more authors.
Sensors and Actuators, B: Chemical | Year: 2013

In this paper, the fabrication method, electrical and fluidic characterization and in vivo testing of the first deep brain silicon multielectrode with monolithically integrated fluidic channel are presented in details. Micromachined silicon probes with monolithically integrated microfluidic channels up to 70 mm length have been realized to perform simultaneous electrical recording and drug delivery in deep brain regions. The achieved cross-sectional dimension of the microchannels is in the range of 5-30 μm, while the length of the channel can be even 70 mm long.Fabrication process and integration of the drug delivery channels and the Pt recording sites are described. Electrical characterization and impedance tuning of the developed probes are also demonstrated. The functionality of the microfluidic channels is verified and the hydrodynamic characteristics (flow rate vs. injection pressure) are measured in the case of several length and cross-sections.Feasibility of our integration concept is proved by locally injected bicuculline in the cortex and in the thalamical regions of rat brain in vivo, while simultaneously recording the electrical signals of the stimulated neurons on four different electrical channels. © 2013 Elsevier B.V. Source

Toth B.,Institute of Cognitive Neuroscience and Psychology | Toth B.,Eotvos Lorand University | Kardos Z.,Institute of Cognitive Neuroscience and Psychology | Kardos Z.,Budapest University of Technology and Economics | And 5 more authors.
Neurobiology of Learning and Memory | Year: 2014

Representations in working memory (WM) are temporary, but can be refreshed for longer periods of time through maintenance mechanisms, thereby establishing their availability for subsequent memory tests. Frontal brain regions supporting WM maintenance operations undergo anatomical and functional changes with advancing age, leading to age related decline of memory functions. The present study focused on age-related functional connectivity changes of the frontal midline (FM) cortex in the theta band (4-8. Hz), related to WM maintenance. In the visual delayed-match-to-sample WM task young (18-26. years, N=20) and elderly (60-71. years. N=16) adults had to memorize sample stimuli consisting of 3 or 5 items while 33 channel EEG recording was performed. The phase lag index was used to quantify connectivity strength between cortical regions. The low and high memory demanding WM maintenance periods were classified based on whether they were successfully maintained (remembered) or unsuccessfully maintained (unrecognized later). In the elderly reduced connectivity strength of FM brain region and decreased performance were observed. The connectivity strength between FM and posterior sensory cortices was shown to be sensitive to both increased memory demands and memory performance regardless of age. The coupling of frontal regions (midline and lateral) and FM-temporal cortices characterized successfully maintained trials and declined with advancing age. The findings provide evidence that a FM neural circuit of theta oscillations that serves a possible basis of active maintenance process is especially vulnerable to aging. © 2014 Elsevier Inc. Source

Mill R.W.,MRC Institute of Hearing Research | Bohm T.M.,Institute of Cognitive Neuroscience and Psychology | Bohm T.M.,Budapest University of Technology and Economics | Bendixen A.,University of Leipzig | And 3 more authors.
PLoS Computational Biology | Year: 2013

Many sound sources can only be recognised from the pattern of sounds they emit, and not from the individual sound events that make up their emission sequences. Auditory scene analysis addresses the difficult task of interpreting the sound world in terms of an unknown number of discrete sound sources (causes) with possibly overlapping signals, and therefore of associating each event with the appropriate source. There are potentially many different ways in which incoming events can be assigned to different causes, which means that the auditory system has to choose between them. This problem has been studied for many years using the auditory streaming paradigm, and recently it has become apparent that instead of making one fixed perceptual decision, given sufficient time, auditory perception switches back and forth between the alternatives-a phenomenon known as perceptual bi- or multi-stability. We propose a new model of auditory scene analysis at the core of which is a process that seeks to discover predictable patterns in the ongoing sound sequence. Representations of predictable fragments are created on the fly, and are maintained, strengthened or weakened on the basis of their predictive success, and conflict with other representations. Auditory perceptual organisation emerges spontaneously from the nature of the competition between these representations. We present detailed comparisons between the model simulations and data from an auditory streaming experiment, and show that the model accounts for many important findings, including: the emergence of, and switching between, alternative organisations; the influence of stimulus parameters on perceptual dominance, switching rate and perceptual phase durations; and the build-up of auditory streaming. The principal contribution of the model is to show that a two-stage process of pattern discovery and competition between incompatible patterns can account for both the contents (perceptual organisations) and the dynamics of human perception in auditory streaming. © 2013 Mill et al. Source

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