Similarity Grouping and Repetition Blindness are Both Influenced by Attention

Previous studies have reported seemingly conflicting results regarding how the amount of stimulus similarity between two simultaneously presented target stimuli impacts perceptual performance. There are many reports of ‘repetition blindness’, where individuals do worse when shown two similar stimuli relative to two different stimuli. On the other hand, there are reports of ‘similarity grouping’, where participants perform better when identifying two similar objects relative to two different objects. This manuscript posits that repetition blindness and similarity grouping coexist and can be elicited in the same subjects in a single task. This not only explains the previous opposite effects of stimulus similarity on task performance, but also provides a unique opportunity to directly compare these opposite effects of stimulus similarity with respect to susceptibility to a modulating factor. Since previous studies have provided inconclusive results on whether attentional relevance can modulate the effect of stimulus similarity on task performance, the current manuscript aims to compare repetition blindness and similarity grouping with respect to their susceptibility to attentional relevance. The results of the first experiment confirmed that both repetition blindness and similarity grouping can be elicited in the same experiment, suggesting that repetition blindness and similarity grouping coexist. The results of the second experiment suggest that both repetition blindness and similarity grouping can be modulated by attentional relevance. These results support the explanation of repetition blindness as a token individuation failure. Furthermore, these results suggest that supposedly pre-attentional grouping mechanisms might not operate as independently from top-down attentional modulations as traditionally thought

Event related potentials reveal that increasing perceptual load leads to increased responses for target stimuli and decreased responses for irrelevant stimuli

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Temporal order processing of syllables in the left parietal lobe

Speech processing requires the temporal parsing of syllable order. Individuals suffering from posterior left hemisphere brain injury often exhibit temporal processing deficits as well as language deficits. Although the right posterior inferior parietal lobe has been implicated in temporal order judgments (TOJs) of visual information, there is limited evidence to support the role of the left inferior parietal lobe (IPL) in processing syllable order. The purpose of this study was to examine whether the left inferior parietal lobe is recruited during temporal order judgments of speech stimuli. Functional magnetic resonance imaging data were collected on 14 normal participants while they completed the following forced-choice tasks: (1) syllable order of multisyllabic pseudowords, (2) syllable identification of single syllables, and (3) gender identification of both multisyllabic and monosyllabic speech stimuli. Results revealed increased neural recruitment in the left inferior parietal lobe when participants made judgments about syllable order compared with both syllable identification and gender identification. These findings suggest that the left inferior parietal lobe plays an important role in processing syllable order and support the hypothesized role of this region as an interface between auditory speech and the articulatory code. Furthermore, a breakdown in this interface may explain some components of the speech deficits observed after posterior damage to the left hemisphere

Enhanced Tactile Performance at the Destination of an Upcoming Saccade

AbstractPrevious work has demonstrated that upcoming saccades influence visual [1, 2] and auditory [3] performance even for stimuli presented before the saccade is executed. These studies suggest a close relationship between saccade generation and visual/auditory attention. Furthermore, they provide support for Rizzolatti et al.'s [4, 5] premotor model of attention, which suggests that the same circuits involved in motor programming are also responsible for shifts in covert orienting (shifting attention without moving the eyes or changing posture). In a series of experiments, we demonstrate that saccade programming also affects tactile perception. Participants made speeded saccades to the left and right side as well as tactile discriminations of up versus down. The first experiment demonstrates that participants were reliably faster at responding to tactile stimuli near the location of upcoming saccades. In our second experiment, we had the subjects cross their hands and demonstrated that the effect occurs in visual space (rather than the early representations of touch). In our third experiment, the tactile events usually occurred on the opposite side of upcoming eye movement. We found that the benefit at the saccade target location vanished, suggesting that this shift is not obligatory but that it may be vetoed on the basis of expectation

Localizing unique and overlapping lesion locations in apraxia of speech and aphasia

Since Darley’s original description of apraxia of speech (AOS; 1968), controversy has centered around its diagnosis, treatment, and lesion location. Behaviors common to AOS are often shared among other communication disorders, complicating clinical management. The current study sought to identify crucial brain damage that causes apraxic speech, as well as errors common in both AOS and aphasia. Results revealed that damage to premotor and supplementary motor areas is unique to AOS, while involvement of temporal lobe areas predicts behaviors attributable to aphasia. These findings contribute to research regarding the neuroanatomical mechanism of AOS, and may ultimately improve differential diagnostic procedures

False Discovery Rate and Localizing Power

False discovery rate (FDR) is commonly used for correction for multiple testing in neuroimaging studies. However, when using two-tailed tests, making directional inferences about the results can lead to vastly inflated error rate, even approaching 100% in some cases. This happens because FDR only provides weak control over the error rate, meaning that the proportion of error is guaranteed only globally over all tests, not within subsets, such as among those in only one or another direction. Here we consider and evaluate different strategies for FDR control with two-tailed tests, using both synthetic and real imaging data. Approaches that separate the tests by direction of the hypothesis test, or by the direction of the resulting test statistic, more properly control the directional error rate and preserve FDR benefits, albeit with a doubled risk of errors under complete absence of signal. Strategies that combine tests in both directions, or that use simple two-tailed p-values, can lead to invalid directional conclusions, even if these tests remain globally valid. To enable valid thresholding for directional inference, we suggest that imaging software should allow the possibility that the user sets asymmetrical thresholds for the two sides of the statistical map. While FDR continues to be a valid, powerful procedure for multiple testing correction, care is needed when making directional inferences for two-tailed tests, or more broadly, when making any localized inference

Localizing lesion locations to predict extent of aphasia recovery

Extensive research has related specific lesion locations to language impairment in aphasia. However, far less work has focused on the patterns of brain damage that predict prognosis in aphasia. The current study examined brain damage as a predictor of language recovery in acute patients with aphasia caused by stroke. Damage to the left posterior middle temporal gyrus (MTG) and left pars triangularis predicted poor recovery of speech production and MTG damage predicted less recovery of speech comprehension. These findings suggest that brain changes associated with language recovery rely on preservation and recruitment of the aforementioned areas in the left hemisphere

Smokers\u27 Neurological Responses to Novel and Repeated Health Warning Labels (HWLs) From Cigarette Packages

Graphic health warning labels (HWLs) depicting bodily injury due to smoking are effective for producing changes in affect, cognition and smoking behavior in adult smokers. However, little is known about the effects of repeated presentation of graphic HWL’s on the aforementioned processes. The goal of this study was to examine neural and behavioral responses to graphic HWL’s and evaluate whether the repeated presentation of graphic HWL’s leads to repetition suppression (RS). Smokers (N = 16) performed an event-related HWL cue task while blood oxygen level dependent (BOLD) signal was collected during a functional magnetic resonance imaging (fMRI) experimental session. Consistent with prior literature, graphic HWL’s, as compared to scrambled images, elicited increased BOLD response in brain regions involved in self-referential and emotion processing. Importantly, BOLD response at sites in this network diminished during repeated presentation of the same HWL. These findings suggest that while novel graphic HWL’smay have a significant effect on smokers’ brain activity, repeated presentationmay lead to muted responses and thus limit their potential to induce behavioral change

Using neuroimaging to classify aphasia

The proper classification of aphasia based on clinical symptoms has been debated for well over a century. Much of the early debates centered on relating localized brain damage to a constellation of speech and language impairments. The premise behind much of this work was based on the notion that lesion-symptom mapping could reveal how language was organized in the brain (Broca, 1861, 1865; Dejarine, 1906; Marie, 1906). Although the principle for classifying aphasia based on specific symptoms has been fervently challenged (e.g. Head, 1926) it is still customary to report aphasia types in clinical studies of aphasia. Similar symptoms in sub-groups of patients suggests a similar pattern of brain damage. Nevertheless, it remains unclear if specific aphasia types can be diagnosed simply based on the location of cortical damage. One way to examine this issue would be to relate lesion patterns to aphasia types using multivariate pattern analysis (MVPA). MVPA of neuroimaging data has been successfully used to diagnose diseases such as dementia, schizophrenia, and Parkinson's disease (Orru et al., 2012). In the present study, we demonstrate how MVPA can be used to predict aphasia type in persons with chronic stroke. Unlike previous studies that perform the analysis on voxels (using MRI scans), we trained a classifier on the proportional damage to brain areas (defined with a brain atlas). In addition, we computed the loadings that reflect the contribution of each brain area to classification

Ipsilesional Biases in Saccades but not Perception after Lesions of the Human Inferior Parietal Lobule

We examined the effects of chronic unilateral lesions to either the inferior parietal lobe, or to the dorsolateral prefrontal cortex including the frontal eye fields (FEFs), upon human visual perception and saccades in temporal-order-judgment (TOJ) tasks. Two visual events were presented on each trial, one in each hemifield at various stimulus onset asynchronies (SOAs). In the saccade task, patients moved their eyes to whichever stimulus attracted gaze first. In the perceptual-manual task, they pressed a button to indicate which stimulus was perceived first. Frontal patients showed appropriate TOJs for visual targets in both tasks. Parietal patients showed appropriate TOJs in the perceptual-manual but not the saccade task; their saccades tended to be ipsilesional unless the contralesional target led substantially. This reveals a bias in saccade choice after parietal damage that cannot be attributed to deficient visual perception. These results challenge previous claims that only anterior lesions produce motoric spatial biases in humans. However, they are in accord with recent neurophysiological evidence for parietal involvement in saccade generation, and also with suggestions that visuomotor transformations in the parietal lobe serving direct spatial motor responses can dissociate from conscious perception as indicated by indirect arbitrary responses