Visuospatial attention allows observers to focus awareness on one or several pieces of information in the visual world. Recent evidence suggests that a network of brain regions including superior frontal, inferior parietal, and superior temporal cortices is involved in the top-down control of visuospatial attention. The goal of this study was to determine whether this network mediates attentional control in different visual frames of reference (FORs), or whether partially separable neural systems underlie attentional orienting in each. Participants were cued to locations defined within viewer- or object-centered FORs and made form discriminations on targets subsequently presented at those locations. Cortical responses to attention-directing cues were recorded with event-related fMRI at 1.5T. Consistent with previous work, a number of brain regions were selectively activated by attention-directing cues including superior frontal, inferior parietal, and superior temporal cortices. Critically, this network was differentially engaged when attention was grounded in different FORs. Specifically, superior temporal regions were more active when spatial attention was deployed within an object-centered FOR, whereas superior frontal regions were more active when spatial attention was deployed within a viewer-centered FOR. Inferior parietal regions were equally responsive to attention-directing cues in both FORs. These results suggest that attentional orienting in different FORs is mediated by an overlapping network of brain regions, but that this network is differentially engaged when attention is deployed in different reference frames.
Visuospatial attention allows observers to focus awareness on one or several pieces of information within the visual world. Recent evidence suggests that superior frontal, inferior parietal and superior temporal cortices are involved in voluntarily orienting visuospatial attention. The goal of these experiments was to determine whether this network mediates the top-down control of attention in different visual frames of reference (FORs), or whether partially separable neural systems underlie attentional orienting in each. Participants were cued to locations defined within viewer- or object-centered FORs and made form discriminations on targets subsequently presented at those locations. Cortical responses to attention-directing cues were recorded with event-related fMRI. Consistent with previous work, a network involving superior frontal, inferior parietal, and superior temporal cortices was activated by attention-directing cues. Critically, this network was differentially engaged when attention was grounded in different FORs. Whereas superior frontal and inferior parietal regions were similarly engaged when attention was deployed in viewer- and object-centered FORs, superior temporal regions were more responsive when attention was deployed in object-centered space. Moreover, similar activity was observed in parietal cortex in both hemispheres across conditions, indicating that right and left parietal cortices were not differentially involved in viewer- and object-based attention. We conclude that an overlapping network of brain regions mediates our ability to orient spatial attention, but that this network is differentially engaged when attention is deployed in different reference frames.
Using traditional (i.e., “slow-rate”) event-related fMRI, we have previously demonstrated that largely overlapping portions of the fronto-parietal attentional network are engaged by voluntary shifts of attention in object-centered as well as viewer-centered visual frames of reference, and that bilateral portions of superior temporal cortex are more strongly engaged when these attentional shifts occur within object-centered space, relative to viewer-centered space. This previous work employed relatively long intervals between the attention-directing cues and subsequent visual targets (i.e., cue-target intervals of 7.5 seconds). Here, we attempt to replicate these findings using rapid, event-related functional MRI at 1.5T. Participants were cued to attend to locations defined within viewer- or object-centered space and made form discriminations on targets subsequently presented at those locations. Brain activity associated specifically with attention-directing cues was analyzed to determine whether partially separable brain systems mediate attentional orienting in different visual frames of reference. The current study uses timing parameters that are more consistent with the majority of published spatial cueing paradigms (i.e., cue-target intervals of 1-2 seconds), and therefore allows more direct comparison of activations with the extant literature. In addition, the shorter cue-target interval reduces demands on working memory operations, allowing us to characterize more accurately the activated regions as involved in attentional control, rather than working memory. Results are discussed with respect to neuropsychological models of reference frame effects in visuospatial attention.
Functional neuroimaging studies have revealed that a bilateral fronto-parietal network is critically involved in the top-down deployment of visuospatial attention in response to endogenous visual cues (e.g., an arrow). Further, a right temporal-parietal region (rTPJ) is engaged for reorienting attention to targets when prior cue information incorrectly predicts target location. Numerous behavioral studies have shown that reorienting attention to an invalidly cued location within an object is faster than reorienting attention to an equidistant location within a different object. These “object-based” effects have been demonstrated repeatedly for reorienting shifts of attention in response to invalidly cued targets, suggesting the involvement of rTPJ. It is unclear, however, whether similar object-based effects are associated with top-down attentional control mechanisms, particularly the fronto-parietal network. In the current study, we provide evidence for distinct, object-based effects associated with the initial deployment of attention in response to valid endogenous cues. Using a modified double-rectangle paradigm (Egly, Driver, & Rafal, 1994), participants performed a simple detection task with predictive (75% valid) pre-cues. Initial shifts of attention could either be within an attended object, or to an equidistant location on a different object. This allowed us to compare initial (top-down) as well as reorienting (bottom-up) shifts of attention to locations either within or between objects. Object-based effects were observed for initial (top-down) shifts of attention in response to valid endogenous cues, suggesting that the fronto-parietal attention control network, like the rTPJ, may also respect such distinctions. Results are discussed in terms of behavioral and neuronal distinctions between top-down and bottom-up control systems.
Functional neuroimaging has revealed a bilateral fronto-parietal network involved in the top-down deployment of visuospatial attention. Further, a right temporal-parietal region (rTPJ) is known to be engaged for reorienting attention to targets when prior cue information incorrectly predicts target location. Behavioral studies have shown that reorienting attention to an invalidly cued location within an object is faster than reorienting attention to an equidistant location within a different object. These “object-based” effects have been demonstrated repeatedly for reorienting shifts of attention, suggesting the involvement of rTPJ. It is unclear, however, whether similar object-based effects are associated with top-down fronto-parietal attentional control mechanisms. Here we provide evidence for distinct, object-based effects associated with the initial deployment of attention in response to spatial pre-cues. Using a modified double-rectangle paradigm, participants performed a simple detection task with either endogenous or exogenous spatial pre-cues. Initial shifts of attention could either be within an attended object, or to an equidistant location on a different object. This allowed us to compare initial (top-down) as well as reorienting (bottom-up) shifts of attention to locations either within or between objects. Object-based effects were observed for initial shifts of attention in response to both exogenous and endogenous cues. In contrast, object-based effects were observed during reorienting shifts of attention only when exogenous cues were used. These findings suggest that the fronto-parietal attention control network employs distinct object-based representations than the rTPJ-mediated reorienting network. Results are further discussed in terms of neuronal distinctions between top-down and bottom-up attentional control networks.
Extensive research has shown that faces appear grotesque when the internal features are inverted, but that this effect is virtually eliminated when the entire face is then rotated 180 degrees. One common explanation for this effect, dubbed the “Thatcher Illusion,” appeals to the hypothesis that configural (holistic) and featural (part-based) processing mechanisms are involved preferentially in processing upright and inverted face, respectively. According to this hypothesis, observers rely more heavily on featural or part-based mechanisms when processing an inverted face, and are therefore less sensitive to the inherently configural distortions that are produced by “thatcherization.” Here we tested a straightforward prediction of this hypothesis concerning the number of features that are manipulated. If inverted face processing relies to a greater extent on part-based processing mechanisms, then the number of features that are distorted should have a greater effect on performance when viewing inverted faces than when viewing upright faces. We tested this prediction by systematically manipulating the number of internal features that were thatcherized while participants judged whether faces were normal or distorted. We also sought to determine the neural correlates of these effects using functional magnetic resonance imaging (fMRI) at 3T. Behavioral results provided strong support for our predictions: performance was virtually unaffected by this manipulation when observers processed upright faces, but was significantly reduced as the number of distorted parts decreased when observers processed inverted faces. Preliminary fMRI data suggest that thatcherization resulted in significantly greater activity in a number of brain regions including the fusiform face area, the amygdala, and the anterior cingulate. These results provide novel evidence concerning the neural correlates of the Thatcher Illusion, and support the hypothesis that the effect is due, at least in part, to the shift from configural to featural processing that accompanies face inversion.
Neuroscientific research involving brain imaging techniques such as functional magnetic resonance imaging (fMRI) has exploded in the past decade. Efforts have been made to incorporate these techniques into scientific curricula, initially at the graduate level and more recently at the advanced undergraduate level. For instance, a number of larger research institutions with in-house fMRI centers have established undergraduate laboratory courses in functional neuroimaging, in which students learn how to design and implement fMRI experiments. To date, however, such courses have not been available to students at smaller institutions that lack MRI scanning facilities. Here I demonstrate the feasibility of implementing such a course at an undergraduate, liberal arts college without internal scanning facilities and with very modest resources. I will discuss an advanced laboratory course in functional MRI that I have recently implemented at Gettysburg College. The course focuses on the use of functional MRI in cognitive neuroscience research, and provides students with the opportunity to learn about the theoretical and technical foundations of fMRI. Lectures cover a variety of topics specific to fMRI, including MR hardware and physics, the physiological basis of the MR signal, data acquisition, fMRI experimental design, and preprocessing and statistical analysis of fMRI data. Laboratory sessions allow students individually to analyze freely available, existing data sets in order to execute the aspects of fMRI data processing and analysis discussed in the lectures. These laboratory sessions are implemented using existing campus computer clusters, requiring only minimal software expenditures. Over the course of the semester, the students also design and implement their own novel fMRI experiment, collecting and analyzing a single pilot data set in each case. The course significantly increases student understanding of neuroscience by providing first-hand experience implementing fMRI, and is the first of its kind to be offered successfully at an undergraduate, liberal arts institution.
Recent evidence suggests that visuospatial transformation processes that are known to rely on dorsal stream visual areas (e.g., mental rotation) are temporarily suppressed during saccade execution, but that other aspects of higher-level visual cognition such as object recognition are relatively unaffected by such eye movements (Irwin & Brockmole, 2000, 2004). Here we examined whether this saccadic suppression generalizes to another visuospatial transformation process, namely, misoriented object recognition. Using fMRI, we recently demonstrated that misoriented object recognition and mental rotation result in distinct viewpoint-dependent brain activity, and that misoriented object recognition is not mediated by dorsal stream visual areas (Wilson & Farah, 2006). We therefore hypothesized that saccadic suppression would occur only for parietally-based visuospatial transformation processes, such as mental rotation, and not for temporally-based visuospatial transformation processes, such as misoriented object recognition. Participants viewed line drawings of common objects that were rotated in the picture plane and either named the object (misoriented object recognition) or judged the direction in which the object was facing (mental rotation). In alternating blocks of trials, participants made these decisions while executing saccades of different length. Saccade distance had distinct effects on response times and eye movements (monitored with a corneal-reflectance eye tracking system) in the object recognition and mental rotation conditions. The current results, along with our previous neuroimaging data, provide converging evidence that misoriented object recognition does not involve parietally-based normalization processes such as mental rotation, but rather relies on viewpoint-dependent mechanisms within the inferior temporal lobe.
Three experiments examined how reference frame impacts the vertical representation of affect. Horizontally positioned participants evaluated words appearing up and down from the environment’s and viewers’ perspective. When up and down in the viewers’ perspective, positive and negative words, respectively, were evaluated faster, suggesting viewers’ (not environment’s) perspective governs affect representation.
An important question concerning visual object recognition is whether spatial transformation processes such as mental rotation are used to recognize objects that are rotated into non-upright orientations. Similar viewpoint effects are often observed behaviorally in mental rotation and rotated object recognition tasks (e.g. longer response times as objects are rotated farther from upright), suggesting overlap between the two. This possibility has been challenged, however, by neuroimaging studies showing different patterns of brain activity in each case. While previous neuroimaging studies have partially differentiated the brain areas involved in mental rotation and rotated object recognition, no studies to date have looked at whether both processes are subject to the same sex-steroid influences. More specifically, extensive research suggests that mental rotation performance differs over the course of the menstrual cycle, with better performance during the menstrual (when estradiol and progesterone levels are relatively low) relative to the midluteal phase (when estradiol and progesterone levels are relatively high). It is unknown, however, whether similar effects occur for rotated object recognition. In this study, female participants performed mental rotation and rotated object recognition tasks during the menstrual and midluteal phases of their menstrual cycle. Results showed that menstrual cycle effects on mental rotation (e.g., better performance during the menstrual relative to the midluteal phase) did not correlate with performance changes during rotated object recognition. These findings complement previous neuroimaging studies, and suggest that mental rotation and rotated object recognition not only rely on distinct brain areas, but are also differentially influenced by sex hormones.
Transcranial direct current stimulation (tDCS) is a non-invasive method of brain stimulation that involves delivering weak, direct electrical currents through the scalp in order to modulate cortical excitability. Applying electrical stimulation in an effort to manipulate brain function has a rich history dating back several hundred years, but only in the past decade has it been incorporated systematically into cognitive neuroscientific research. Indeed, the past five years have seen an explosion in the number of publications involving tDCS (from fewer than 20 in 2006 to more than 220 in 2011). As with any new research tool in neuroscience, it is important to introduce students to this methodology at the undergraduate level, to improve neuroscientific literacy and to prepare them better for graduate-level education in the fields of neuroscience and medicine. Here, I present a novel undergraduate laboratory course in tDCS that I recently implemented at Gettysburg College (the first to be offered at the undergraduate level). I also demonstrate the feasibility of implementing an undergraduate laboratory course in tDCS at other institutions. The course focused on the use of tDCS in cognitive neuroscience research and provided students with the opportunity to learn about the theoretical and technical foundations of tDCS. Lectures covered a variety of topics specific to tDCS, including tDCS hardware and physics as well as the physiological basis of the neuromodulatory effects of tDCS. Students also read and discussed primary research articles that used tDCS to investigate specific topics within cognitive neuroscience (e.g., working memory, emotion, and language). Additionally, students designed and implemented their own novel tDCS experiment over the course of the semester (including data collection and statistical analyses). Student evaluations from the course were compared with those from previous laboratory courses involving brain imaging (fMRI) at Gettysburg College. Statistical analyses revealed that students reported being significantly more interested in neuroscience research as a result of the tDCS course and significantly better prepared for advanced and graduate-level coursework in neuroscience as a result of the tDCS course, compared to previous fMRI laboratory courses at Gettysburg. Given that tDCS is a safe and relatively inexpensive method of modulating brain function, the success of the present course demonstrates the advantages of incorporating non-invasive electrical brain stimulation into the undergraduate neuroscience curriculum.
Does the human visual system contain a specialized system for face recognition, not used for the recognition of other objects? This question was addressed using the “face inversion effect” which refers to the loss of our normal proficiency at face perception when faces are inverted. We found that a prosopagnosic subject paradoxically performed better at matching inverted faces than upright faces, the opposite of the normal “face inversion effect”. The fact that his impairment was most pronounced with the stimuli for which normal subjects show the greatest proficiency in face perception provides evidence of a neurologically localized module for upright face recognition in humans. An additional implication of these data is that specialized systems may control behavior even when they are malfunctioning and therefore maladeaptive, consistent with the mandatory operation of such systems according to the “modularity” hypothesis of the cognitive architecture.
There is growing evidence that face recognition is “special” but less certainty concerning the way in which it is special. The authors review and compare previous proposals and their own more recent hypothesis, that faces are recognized “holistically” (i.e., using relatively less part decomposition than other types of objects). This hypothesis, which can account for a variety of data from experiments on face memory, was tested with 4 new experiments on face perception. A selective attention paradigm and a masking paradigm were used to compare the perception effaces with the perception of inverted faces, words, and houses. Evidence was found of relatively less part-based shape representation for faces. The literatures on machine vision and single unit recording in monkey temporal cortex are also reviewed for converging evidence on face representation. The neuropsychological literature is reviewed for evidence on the question of whether face representation differs in degree or kind from the representation of other types of objects.
Obsessive-compulsive disorder (OCD) has been studied extensively in recent years, with increased emphasis on understanding OCD’s biological substrates. There has been significant progress in documenting abnormal brain function in OCD patients, particularly in the orbitofrontal cortex, basal ganglia, and thalamus. Similar progress has broadened our understanding of the cognitive and behavioral manifestations of the disorder, including deficits in set shifting, hyperattention,and visuospatial construction abilities. Unfortunately, these results have not been replicated consistently.This report comprises a review of previous attempts to characterize the neurobiology and neuropsychology of OCD, and a discussion of several factors in OCD research that can help to explain previous inconsistencies.
One popular model of object recognition claims that the visual system typically describes objects using view-specific representations, but that viewpoint-invariant representations are used when objects can be specified uniquely by the arrangement of parts along a single dimension. In a series of three naming experiments using novel, two-dimensional line drawings, we test this hypothesis against alternative accounts of when viewpoint-invariant representations are used during the recognition of upright and viewplane-rotated objects. Experiments 1 and 2 demonstrate that the number of dimensions along which featural information must be represented is the only stimulus feature that influences the type of representation used, consistent with the Tarr and Pinker model. Experiment 3, however, reveals that the use of viewpoint-invariant representations during recognition is not driven purely by stimulus features, and is at least partly under voluntary control. These data suggest that viewpoint-invariant representations are not automatically invoked by the visual system when the requisite stimulus features are present. Rather, our results suggest that top-down control processes, as well as bottom-up stimulus features, jointly determine the conditions under which the visual system uses viewpoint-invariant representations during visual recognition.
In the following manuscript I demonstrate the feasibility of implementing a functional magnetic resonance imaging (fMRI) laboratory course at an undergraduate liberal arts college without internal scanning facilities and with very modest resources, based on my recent experience implementing such a course using the textbook Functional Magnetic Resonance Imaging (Sinauer Associates, Inc., 2004). I discuss how specific topics were incorporated into lectures, including MR hardware and physics, the physiological basis of the MR signal, data acquisition, fMRI experimental design, and the preprocessing and statistical analysis of fMRI data. I also discuss how I implemented laboratory sessions that allowed students individually to analyze freely available, existing fMRI data sets. I summarize how these laboratory sessions were implemented using existing campus computer clusters, requiring only minimal software expenditures. Finally, I describe how students were able to design their own research project and collect pilot fMRI data through collaborations with researchers at a larger institution. This type of course can be implemented at virtually any institution with proper planning and preparation and is an excellent opportunity to provide advanced undergraduate students with a first-hand appreciation of one of the fastest growing techniques for research in cognitive neuroscience.
Neuropsychological research has consistently demonstrated that spatial attention can be anchored in one of several coordinate systems, including those defined with respect to an observer (viewer-centered), to the gravitational vector (environment-centered), or to individual objects (object-centered). In the present study, we used hemodynamic correlates of brain function to investigate the neural systems that mediate attentional control in two competing reference frames. Healthy volunteers were cued to locations defined in either viewer-centered or object-centered space to discriminate the shape of visual targets subsequently presented at the cued locations. Brain responses to attention-directing cues were quantified using event-related functional magnetic resonance imaging. A fronto-parietal control network was activated by attention-directing cues in both reference frames. Voluntary shifts of attention produced increased neural activity bilaterally in several cortical regions including the intraparietal sulcus, anterior cingulate cortex, and the frontal eye fields. Of special interest was the observation of hemispheric asymmetries in parietal cortex; there was significantly greater activity in left parietal cortex than in the right, but this asymmetry was more pronounced for object-centered shifts of attention, relative to viewer-centered shifts of attention. Measures of behavioral performance did not differ significantly between the two reference frames. We conclude that a largely overlapping, bilateral, cortical network mediates our ability to orient spatial attention in multiple coordinate systems, and that the left intraparietal sulcus plays an additional role for orienting in object-centered space. These results provide neuroimaging support for related claims based on findings of deficits in object-based orienting in patients with left parietal lesions.
This article describes the feasibility of implementing a functional
magnetic resonance imaging (fMRI) laboratory course at an undergraduate-
focused institution without internal scanning facilities.
I discuss how to incorporate specific functional brain imaging
topics into lectures, how to design and implement laboratory sessions
that allow students to analyze existing fMRI data sets, and
how to incorporate empirical research projects involving novel
fMRI data collection into the course through collaborations with
researchers at larger institutions. This type of course is possible at
virtually any institution and provides an excellent opportunity for
advanced undergraduate students to gain first-hand research experience
in cognitive neuroscience.
A fundamental but unanswered question about the human visual system concerns the way in which misoriented objects are recognized. One hypothesis maintains that representations of incoming stimuli are transformed via parietally based spatial normalization mechanisms (eg mental rotation) to match view-specific representations in long-term memory. Using fMRI, we tested this hypothesis by directly comparing patterns of brain activity evoked during classic mental rotation and misoriented object recognition involving everyday objects. BOLD activity increased systematically with stimulus rotation within the ventral visual stream during object recognition and within the dorsal visual stream during mental rotation. More specifically, viewpoint-dependent activity was significantly greater in the right superior parietal lobule during mental rotation than during object recognition. In contrast, viewpoint-dependent activity was significantly greater in the right fusiform gyrus during object recognition than during mental rotation. In addition to these differences in viewpoint-dependent activity, object recognition and mental rotation produced distinct patterns of brain activity, independent of stimulus rotation: object recognition resulted in greater overall activity within ventral stream visual areas and mental rotation resulted in greater overall activity within dorsal stream visual areas. The present results are inconsistent with the hypothesis that misoriented object recognition is mediated by structures within the parietal lobe that are known to be involved in mental rotation.
Observers cannot accurately discriminate the top halves of two sequentially presented three-letter words. One interpretation of this effect is that words, like faces, are processed holistically. Here we show, in three simple experiments, that this phenomenon is more consistent with the hypothesis that letters, not words, are processed holistically.