Neural Dynamics of Motion Processing and Speed Discrimination

A neural network model of visual motion perception and speed discrimination is presented. The model shows how a distributed population code of speed tuning, that realizes a size-speed correlation, can be derived from the simplest mechanisms whereby activations of multiple spatially short-range filters of different size are transformed into speed-tuned cell responses. These mechanisms use transient cell responses to moving stimuli, output thresholds that covary with filter size, and competition. These mechanisms are proposed to occur in the Vl→7 MT cortical processing stream. The model reproduces empirically derived speed discrimination curves and simulates data showing how visual speed perception and discrimination can be affected by stimulus contrast, duration, dot density and spatial frequency. Model motion mechanisms are analogous to mechanisms that have been used to model 3-D form and figure-ground perception. The model forms the front end of a larger motion processing system that has been used to simulate how global motion capture occurs, and how spatial attention is drawn to moving forms. It provides a computational foundation for an emerging neural theory of 3-D form and motion perception.Office of Naval Research (N00014-92-J-4015, N00014-91-J-4100, N00014-95-1-0657, N00014-95-1-0409, N00014-94-1-0597, N00014-95-1-0409); Air Force Office of Scientific Research (F49620-92-J-0499); National Science Foundation (IRI-90-00530

Neural Dynamics of Motion Grouping: From Aperture Ambiguity to Object Speed and Direction

A neural network model of visual motion perception and speed discrimination is developed to simulate data concerning the conditions under which components of moving stimuli cohere or not into a global direction of motion, as in barberpole and plaid patterns (both Type 1 and Type 2). The model also simulates how the perceived speed of lines moving in a prescribed direction depends upon their orientation, length, duration, and contrast. Motion direction and speed both emerge as part of an interactive motion grouping or segmentation process. The model proposes a solution to the global aperture problem by showing how information from feature tracking points, namely locations from which unambiguous motion directions can be computed, can propagate to ambiguous motion direction points, and capture the motion signals there. The model does this without computing intersections of constraints or parallel Fourier and non-Fourier pathways. Instead, the model uses orientationally-unselective cell responses to activate directionally-tuned transient cells. These transient cells, in turn, activate spatially short-range filters and competitive mechanisms over multiple spatial scales to generate speed-tuned and directionally-tuned cells. Spatially long-range filters and top-down feedback from grouping cells are then used to track motion of featural points and to select and propagate correct motion directions to ambiguous motion points. Top-down grouping can also prime the system to attend a particular motion direction. The model hereby links low-level automatic motion processing with attention-based motion processing. Homologs of model mechanisms have been used in models of other brain systems to simulate data about visual grouping, figure-ground separation, and speech perception. Earlier versions of the model have simulated data about short-range and long-range apparent motion, second-order motion, and the effects of parvocellular and magnocellular LGN lesions on motion perception.Office of Naval Research (N00014-920J-4015, N00014-91-J-4100, N00014-95-1-0657, N00014-95-1-0409, N00014-91-J-0597); Air Force Office of Scientific Research (F4620-92-J-0225, F49620-92-J-0499); National Science Foundation (IRI-90-00530

Something for Nothing: Universal Basic Income and the Value of Work Beyond Incentives

Proponents and opponents of a universal basic income all acknowledge that the most significant political challenge to its adoption in the United States is that a universal basic income would not have a work requirement attached. Often, this is characterized as a problem involving incentives—the availability of a universal basic income would cause many people to stop working (or significantly curtail the number of hours that they work) and simply live off the universal basic income. This Article makes three contributions to the literature related to a universal basic income: First, it provides a typology for understanding the many reasons for valuing work; second, it argues that the United States is unlikely to implement a universal basic income because a universal basic income does not account for several aspects of the value of work; and, third, it argues that advocates of a universal basic income should instead focus on the more modest goal of redefining the activities that constitute work and broadening the social safety net by expanding existing policies through the use of a broader definition of work. This Article proposes that the value of work in American political culture has four primary dimensions: (1) reciprocity, that one receives rewards for one’s labor, that one gets what one gives and that no one should be a free rider, one who gets but does not give; (2) calling or vocation, that work is a calling or vocation that one should have or pursue, and that only those that have or pursue such a calling or vocation have moral standing; (3) self-sufficiency, that work promotes self-sufficiency, which is a necessary component of liberty and which is necessary to avoid dependency; and (4) incentives, of an economic kind, that society should encourage work because it increases the size of the economic pie. These categories provide a new framework for thinking about the value of work and for evaluating policies that relate to the working lives of Americans. As an alternative to the adoption of a universal basic income, this Article proposes that proponents of a universal basic income should focus on expanding and redefining current policies, such as the Earned Income Tax Credit so that they more closely resemble a participation income. In fact, a broader definition of work has even been used in recent conservative policy ideas, such as the Medicaid work requirements that some states have introduced, which include within their definition of work the activities of education, job training, and community service. This Article closes with an outline of a proposal to adopt an expansion of the Earned Income Tax Credit that resembles a participation income and addresses each of the dimensions of the value of work

Multimodality Imaging in Carotid Web

Purpose: Carotid web (CaW) is an underrecognized cause of cryptogenic stroke in young patients. The optimal imaging for CaW is unknown. We aim to evaluate the diagnostic accuracy of diverse imaging modalities for the diagnosis of CaW.Methods: Retrospective analysis of institutional neurovascular database was performed to identify patients with multimodal (CT angiogram–CTA, digital subtraction angiogram–DSA, and/or ultrasound–US) imaging diagnosis of CaW or atherosclerosis. Baseline clinical demographics were recorded. Blinded image analysis was performed for each imaging modality by separate readers. Discrepancies were settled by consensus. Two-sided Cohen's Kappa (κ) coefficient was used to evaluate the inter-rater agreement for the etiological diagnosis between imaging modalities.Results: Thirty patients/60 carotids were evaluated by CTA and 55 carotids were included. Patients with symptomatic CaW (n = 20), compared to individuals with atherosclerosis (n = 10), were younger (49 ± 9 vs. 60 ± 8 years; p < 0.01), more commonly female (75% vs. 30%; p = 0.01), and less frequently presented vascular risk factors: Hypertension (40% vs. 100%; p < 0.01), hyperlipidemia (0% vs. 50%; p < 0.01), diabetes (10% vs. 40%; p = 0.05), and smoking (5% vs. 70%; p < 0.01). High inter-rater correlation strength existed for CTA (n = 55; κ = 0.88; p < 0.0001) and DSA (n = 28; κ = 0.86, p < 0.0001) readers for lesion diagnosis while US inter-rater agreement was lower (κ = 0.553; p = 0.001). Across modalities CTA and DSA shared very high strength of agreement (κ = 0.92; p < 0.0001), compared to a less pronounced agreement between US and CTA (κ = 0.553; p = 0.001). The strength of correlation between DSA-CTA was significantly more robust as compared to US-CTA (Z = 3.58; p = 0.0003).Conclusion: CTA and DSA demonstrated comparable and superior performance as compared to US in the diagnosis of CaW

Looking the Part: Social Status Cues Shape Race Perception

It is commonly believed that race is perceived through another's facial features, such as skin color. In the present research, we demonstrate that cues to social status that often surround a face systematically change the perception of its race. Participants categorized the race of faces that varied along White–Black morph continua and that were presented with high-status or low-status attire. Low-status attire increased the likelihood of categorization as Black, whereas high-status attire increased the likelihood of categorization as White; and this influence grew stronger as race became more ambiguous (Experiment 1). When faces with high-status attire were categorized as Black or faces with low-status attire were categorized as White, participants' hand movements nevertheless revealed a simultaneous attraction to select the other race-category response (stereotypically tied to the status cue) before arriving at a final categorization. Further, this attraction effect grew as race became more ambiguous (Experiment 2). Computational simulations then demonstrated that these effects may be accounted for by a neurally plausible person categorization system, in which contextual cues come to trigger stereotypes that in turn influence race perception. Together, the findings show how stereotypes interact with physical cues to shape person categorization, and suggest that social and contextual factors guide the perception of race

Effect of extracranial lesion severity on outcome of endovascular thrombectomy in patients with anterior circulation tandem occlusion: analysis of the TITAN registry

Introduction Endovascular treatment (EVT) for tandem occlusion (TO) of the anterior circulation is complex but effective. The effect of extracranial internal carotid artery (EICA) lesion severity on the outcomes of EVT is unknown. In this study we investigated the effect of EICA lesion severity on the outcomes of tandem occlusion EVT. Methods A multicenter retrospective TITAN (Thrombectomy In TANdem lesions) study that included 18 international endovascular capable centers was performed. Patients who received EVT for atherosclerotic TO with or without EICA lesion intervention were included. Patients were divided into two groups based on the EICA lesion severity (high-grade stenosis (>= 90% North American Symptomatic Carotid Endarterectomy Trial) vs complete occlusion). Outcome measures included the 90-day clinical outcome (modified Rankin Scale score (mRS)), angiographic reperfusion (modified Thrombolysis In Cerebral Ischemia (mTICI) at the end of the procedure), procedural complications, and intracranial hemorrhage at 24 hours follow-up. Results A total of 305 patients were included in the study, of whom 135 had complete EICA occlusion and 170 had severe EICA stenosis. The EICA occlusion group had shorter mean onset-to-groin time (259 +/- 120 min vs 305 +/- 202 min;p=0.037), more patients with diabetes, and fewer with hyperlipidemia. With respect to the outcome, mTICI 2b-3 reperfusion was lower in the EICA occlusion group (70% vs 81%;p=0.03). The favorable outcome (90-day mRS 0-2), intracerebral hemorrhage and procedural complications were similar in both groups. Conclusion Atherosclerotic occlusion of the EICA in acute tandem strokes was associated with a lower rate of mTICI 2b-3 reperfusion but similar functional and safety outcomes when compared with high-grade EICA stenosis