533 research outputs found

    Change blindness: eradication of gestalt strategies

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    Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

    Thalamic theta phase alignment predicts human memory formation and anterior thalamic cross-frequency coupling

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    Previously we reported electrophysiological evidence for a role for the anterior thalamic nucleus (ATN) in human memory formation (Sweeney-Reed et al., 2014). Theta-gamma cross-frequency coupling (CFC) predicted successful memory formation, with the involvement of gamma oscillations suggesting memory-relevant local processing in the ATN. The importance of the theta frequency range in memory processing is well-established, and phase alignment of oscillations is considered to be necessary for synaptic plasticity. We hypothesized that theta phase alignment in the ATN would be necessary for memory encoding. Further analysis of the electrophysiological data reveal that phase alignment in the theta rhythm was greater during successful compared with unsuccessful encoding, and that this alignment was correlated with the CFC. These findings support an active processing role for the ATN during memory formation

    The neurophysiology of intersensory selective attention and task switching

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    Our ability to selectively attend to certain aspects of the world and ignore others is fundamental to our day-to-day lives. The need for selective attention stems from capacity limitations inherent in our perceptual and cognitive processing architecture. Because not every elemental piece of our environment can be fully processed in parallel, the nervous system must prioritize processing. This prioritization is generally referred to as selective attention. Meanwhile, we are faced with a world that is constantly in flux, such that we have to frequently shift our attention from one piece of the environment to another and from one task to another. This process is generally referred to as task-switching. Neural oscillations in the alpha band (~8-14 Hz) have been shown to index the distribution of selective attention, and there is increasing evidence that oscillations in this band are in fact utilized by the nervous system to suppress distracting, task-irrelevant information. In order to elaborate on what is known of the function of alpha oscillations as well as current models of both intersensory selective attention and task switching, I investigated the dynamics of alpha amplitude modulations within the context of intersenory selective attention and task switching in neurologically typical young adults. Participants were alternately cued to attend to either the visual or auditory aspect of a compound audio-visual stimulus while high-density electroencephalography was recorded. It is typically found that alpha power increases over parieto-occipital cortices when attention is directed away from the visual modality and to the auditory modality. I report evidence that alpha oscillations play a role in task-switching (e.g., when switching from attending the visual task versus repeating this task), specifically as biasing signals, that may operate to re-weight competition among two tasks-sets. I further investigated the development of these same processes in school-aged children and adolescents. While exhibiting typical patterns of alpha modulations relevant to selective attention, Young school-aged children (8-12 years), compared to older participants, did not demonstrate specific task switching modulation of alpha oscillations, suggesting that this process does not fully develop until late adolescence. Finally, children and adolescents on the autism spectrum failed altogether to exhibit differentiation of alpha power between attend-visual and attend-auditory conditions--an effect present in age and IQ matched controls--suggesting that ASD individuals may have a deficit in the overall top-down deployment of alpha oscillatory biasing signals. This could result in an inability to ignore distracting information in the environment, leading to an overwhelming, disordered experience of the world, resulting in profound effects on the both social interaction and cognitive development. Altogether, these findings add to growing evidence that alpha oscillations serve as domain general biasing signals and are integral to our flexible goal-oriented behavior. Furthermore, the flexible use of these biasing signals in selective attention and task switching develops over a protracted period, and appears to be aberrant in autism spectrum disorder

    Activation of the Left Inferior Frontal Gyrus in the First 200 ms of Reading: Evidence from Magnetoencephalography (MEG)

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    BACKGROUND: It is well established that the left inferior frontal gyrus plays a key role in the cerebral cortical network that supports reading and visual word recognition. Less clear is when in time this contribution begins. We used magnetoencephalography (MEG), which has both good spatial and excellent temporal resolution, to address this question. METHODOLOGY/PRINCIPAL FINDINGS: MEG data were recorded during a passive viewing paradigm, chosen to emphasize the stimulus-driven component of the cortical response, in which right-handed participants were presented words, consonant strings, and unfamiliar faces to central vision. Time-frequency analyses showed a left-lateralized inferior frontal gyrus (pars opercularis) response to words between 100-250 ms in the beta frequency band that was significantly stronger than the response to consonant strings or faces. The left inferior frontal gyrus response to words peaked at approximately 130 ms. This response was significantly later in time than the left middle occipital gyrus, which peaked at approximately 115 ms, but not significantly different from the peak response in the left mid fusiform gyrus, which peaked at approximately 140 ms, at a location coincident with the fMRI-defined visual word form area (VWFA). Significant responses were also detected to words in other parts of the reading network, including the anterior middle temporal gyrus, the left posterior middle temporal gyrus, the angular and supramarginal gyri, and the left superior temporal gyrus. CONCLUSIONS/SIGNIFICANCE: These findings suggest very early interactions between the vision and language domains during visual word recognition, with speech motor areas being activated at the same time as the orthographic word-form is being resolved within the fusiform gyrus. This challenges the conventional view of a temporally serial processing sequence for visual word recognition in which letter forms are initially decoded, interact with their phonological and semantic representations, and only then gain access to a speech code

    Inventing episodic memory : a theory of dorsal and ventral hippocampus

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    Mapping the time-course and content of visual predictions with a novel object-scene associative memory paradigm

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    In the current thesis, we present a series of three ERP experiments investigating the time-course and nature of contextual facilitation effects in visual object processing. In all three experiments, participants studied novel object-scene pairs in a paired associate memory paradigm. At test, we presented the scene first, followed after a delay by the test object, which either matched or mismatched the scene. We manipulated two key factors. 1) In all three experiments, we manipulated the severity of contextual mismatch between the presented object and the scene, including categorical violations as well as more subtle visual distortions. In this way, we probed the level of detail at which participants were reactivating the contextually-congruent target object in response to the scene. 2) We manipulated the scene preview timing parameters both between subjects (Experiments 2.1 and 3.1) and within subjects (Experiment 3.2). Our rationale for doing this was as follows. Rather than assuming that contextual facilitation effects reflect an entirely predictive or reactive/integrative process, we tested the hypothesis that contextual facilitation was predictive in nature. If the contextual facilitation was entirely integrative (i.e., people waited until the object was presented before relating it to the scene context), we might expect that the amount of scene preview time would not modulate contextual facilitation effects. What we found instead is that allowing for additional scene preview time leads to enhanced contextual facilitation effects, suggesting that participants are using the additional time that they are observing the scene alone (beyond 200 ms, which is sufficient to extract the gist of the scene) to prepare to process the upcoming object and determine whether it matches the scene. We strengthened our findings by testing this both between subjects using only two time points, and within subjects using a parametric gradation of preview times (which also allowed us to test if our findings generalized to cases of temporal uncertainty). We also took advantage of our use of ERPs to examine dependent measures tied to specific stages of cognition. We particularly focus our analysis and discussion on contextual priming of higher-level visual features, examining how contextual congruency modulates amplitude of the N300 component under various conditions and timing constraints. We also present a set of novel visual similarity analyses relying on V1-like features, which allow us to test for context effects on visual object understanding in a component-neutral fashion. Lastly, we present analyses of context effects on other components of the waveform: the N400, as an index of semantic priming, and the LPC, as an index of response-related processing. Overall, our findings are consistent with a predictive account, in which participants use scene information to preactivate features of the upcoming object (including higher-level visual form features, as well as semantic features) in order to facilitate visual object understanding. Future work will further disentangle predictive vs. integrative processing accounts of contextual facilitation effects on visual object processing

    A Cognitive Neuroscience Examination Of Rhythm And Reading And Their Translation To Neurological Conditions

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    The goal of the current research was to provide a novel and comprehensive examination of the connection between rhythm and reading through the combination of multiple experimental stimuli, and to translate the reading aloud research to neurological patients. Both speech and music perception/production involve sequences of rhythmic events that unfold over time, and the presence of rhythm in both processes has motivated researchers to consider whether musical and speech rhythm engage shared neural regions (Patel, 2008), and whether musical rhythm can influence speech processing (Cason & Schön, 2012). The experimental paradigm involved examining whether reading aloud is affected by the presentation of a rhythmic prime that was either congruent or incongruent with the syllabic stress of the target letter string. The experiments in Chapter 2 used targets that were words that placed the stress on either the first or second syllable (practice vs. police), as well as their corresponding pseudohomophones (praktis vs. poleese), which allowed us to compare lexical and sublexical reading, respectively. In Chapter 3, the experiments involved a paradigm in which target words have stress on the first syllable for nouns, and on the second syllable for verbs. Thus, the design used identical noun-verb word pairs (conflict vs. conflict), as well as their corresponding pseudohomophones (konflikt vs. konflikt). The results from the behavioural experiments demonstrated that naming reaction times were faster for words and pseudohomophones when the rhythmic prime was congruent with the syllabic stress, and slower when the rhythmic prime was incongruent, which suggests that a rhythmic prime matched to the syllabic stress of a letterstring aids reading processes. Functional magnetic resonance imaging (fMRI) was also used in Chapters 2 and 3 to test whether a network involving the putamen is involved in the effect of rhythm on reading aloud. The fMRI results revealed that a network involving the putamen is associated with the effect of congruency between rhythmic stress and syllabic stress on reading aloud, which is consistent with previous literature that has shown this region is involved in reading, rhythm processing, and predicting upcoming events. Chapter 4 was to provide a behavioural and neuroanatomical examination of reading processes in two patients. Case Study 1 examined the effect of rhythmic priming on reading aloud in a patient with Parkinson’s disease (PD), given that these patients exhibit abnormalities in the putamen, which has been associated with rhythm and reading processes. The patient demonstrated the same behavioural effect as normal participants, whereby individuals benefited from the rhythm prime being congruent with the syllabic stress of the target letter string, and the fMRI results revealed that despite disruptions in basal ganglia functioning following PD, there was still activation in the putamen for reading real words. Case Study 2 examined a patient with intractable left temporal lobe epilepsy (TLE) who was undergoing a temporal lobectomy that involved removing regions of the left temporal lobe that are often thought to be important in language processing. The fMRI results showed that all four reading tasks activated the right posterior occipitotemporal region in the ventral visual stream, confirming the right hemisphere dominance in this patient. Together, these findings have implications for developing neurobiological models of reading, translation to localization of function in neurological conditions such as PD and TLE, and may also reveal potential remedial applications for treating speech deficits in patient populations, such as Parkinson’s disease, stuttering, aphasia, and dyslexia

    Neural correlates of true and false memory in mild cognitive impairment

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    The goal of this research was to investigate the changes in neural processing in mild cognitive impairment. We measured phase synchrony, amplitudes, and event-related potentials in veridical and false memory to determine whether these differed in participants with mild cognitive impairment compared with typical, age-matched controls. Empirical mode decomposition phase locking analysis was used to assess synchrony, which is the first time this analysis technique has been applied in a complex cognitive task such as memory processing. The technique allowed assessment of changes in frontal and parietal cortex connectivity over time during a memory task, without a priori selection of frequency ranges, which has been shown previously to influence synchrony detection. Phase synchrony differed significantly in its timing and degree between participant groups in the theta and alpha frequency ranges. Timing differences suggested greater dependence on gist memory in the presence of mild cognitive impairment. The group with mild cognitive impairment had significantly more frontal theta phase locking than the controls in the absence of a significant behavioural difference in the task, providing new evidence for compensatory processing in the former group. Both groups showed greater frontal phase locking during false than true memory, suggesting increased searching when no actual memory trace was found. Significant inter-group differences in frontal alpha phase locking provided support for a role for lower and upper alpha oscillations in memory processing. Finally, fronto-parietal interaction was significantly reduced in the group with mild cognitive impairment, supporting the notion that mild cognitive impairment could represent an early stage in Alzheimer’s disease, which has been described as a ‘disconnection syndrome’
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