Perceptual “Read-Out” of Conjoined Direction and Disparity Maps in Extrastriate Area MT

Cortical neurons are frequently tuned to several stimulus dimensions, and many cortical areas contain intercalated maps of multiple variables. Relatively little is known about how information is “read out” of these multidimensional maps. For example, how does an organism extract information relevant to the task at hand from neurons that are also tuned to other, irrelevant stimulus dimensions? We addressed this question by employing microstimulation techniques to examine the contribution of disparity-tuned neurons in the middle temporal (MT) visual area to performance on a direction discrimination task. Most MT neurons are tuned to both binocular disparity and the direction of stimulus motion, and MT contains topographic maps of both parameters. We assessed the effect of microstimulation on direction judgments after first characterizing the disparity tuning of each stimulation site. Although the disparity of the stimulus was irrelevant to the required task, we found that microstimulation effects were strongly modulated by the disparity tuning of the stimulated neurons. For two of three monkeys, microstimulation of nondisparity-selective sites produced large biases in direction judgments, whereas stimulation of disparity-selective sites had little or no effect. The binocular disparity was optimized for each stimulation site, and our result could not be explained by variations in direction tuning, response strength, or any other tuning property that we examined. When microstimulation of a disparity-tuned site did affect direction judgments, the effects tended to be stronger at the preferred disparity of a stimulation site than at the nonpreferred disparity, indicating that monkeys can selectively monitor direction columns that are best tuned to an appropriate conjunction of parameters. We conclude that the contribution of neurons to behavior can depend strongly upon tuning to stimulus dimensions that appear to be irrelevant to the current task, and we suggest that these findings are best explained in terms of the strategy used by animals to perform the task

Orbitofrontal Cortex Value Signals Depend on Fixation Location during Free Viewing

In the natural world, monkeys and humans judge the economic value of numerous competing stimuli by moving their gaze from one object to another, in a rapid series of eye movements. This suggests that the primate brain processes value serially, and that value-coding neurons may be modulated by changes in gaze. To test this hypothesis, we presented monkeys with value-associated visual cues and took the unusual step of allowing unrestricted free viewing while we recorded neurons in the orbitofrontal cortex (OFC). By leveraging natural gaze patterns, we found that a large proportion of OFC cells encode gaze location and, that in some cells, value coding is amplified when subjects fixate near the cue. These findings provide the first cellular-level mechanism for previously documented behavioral effects of gaze on valuation and suggest a major role for gaze in neural mechanisms of valuation and decision-making under ecologically realistic conditions

Orbitofrontal Cortex Value Signals Depend on Fixation Location during Free Viewing

In the natural world, monkeys and humans judge the economic value of numerous competing stimuli by moving their gaze from one object to another, in a rapid series of eye movements. This suggests that the primate brain processes value serially, and that value-coding neurons may be modulated by changes in gaze. To test this hypothesis, we presented monkeys with value-associated visual cues and took the unusual step of allowing unrestricted free viewing while we recorded neurons in the orbitofrontal cortex (OFC). By leveraging natural gaze patterns, we found that a large proportion of OFC cells encode gaze location and, that in some cells, value coding is amplified when subjects fixate near the cue. These findings provide the first cellular-level mechanism for previously documented behavioral effects of gaze on valuation and suggest a major role for gaze in neural mechanisms of valuation and decision-making under ecologically realistic conditions

Reaction of preschool children to the birth of a sibling

The experience of becoming and having a sibling is a common situation for many preschool children. In order to clarify the implications of such an event for the older preschool child, the authors have surveyed the literature and interviewed a series of families where there was a second or third birth. This is a preliminary communication where a broad overview of the many variables involved is sought. Varied techniques for preparing the older preschool sibling were observed, as were varied coping mechanisms employed by the older child in adjusting to the change in his family status. Fourteen variables are discussed, and suggestions are made for further research.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43963/1/10578_2005_Article_BF01441311.pd

Integration of Sensory and Reward Information during Perceptual Decision-Making in Lateral Intraparietal Cortex (LIP) of the Macaque Monkey

Single neurons in cortical area LIP are known to carry information relevant to both sensory and value-based decisions that are reported by eye movements. It is not known, however, how sensory and value information are combined in LIP when individual decisions must be based on a combination of these variables. To investigate this issue, we conducted behavioral and electrophysiological experiments in rhesus monkeys during performance of a two-alternative, forced-choice discrimination of motion direction (sensory component). Monkeys reported each decision by making an eye movement to one of two visual targets associated with the two possible directions of motion. We introduced choice biases to the monkeys' decision process (value component) by randomly interleaving balanced reward conditions (equal reward value for the two choices) with unbalanced conditions (one alternative worth twice as much as the other). The monkeys' behavior, as well as that of most LIP neurons, reflected the influence of all relevant variables: the strength of the sensory information, the value of the target in the neuron's response field, and the value of the target outside the response field. Overall, detailed analysis and computer simulation reveal that our data are consistent with a two-stage drift diffusion model proposed by Diederich and Bussmeyer [1] for the effect of payoffs in the context of sensory discrimination tasks. Initial processing of payoff information strongly influences the starting point for the accumulation of sensory evidence, while exerting little if any effect on the rate of accumulation of sensory evidence

Can Monkeys Choose Optimally When Faced with Noisy Stimuli and Unequal Rewards?

We review the leaky competing accumulator model for two-alternative forced-choice decisions with cued responses, and propose extensions to account for the influence of unequal rewards. Assuming that stimulus information is integrated until the cue to respond arrives and that firing rates of stimulus-selective neurons remain well within physiological bounds, the model reduces to an Ornstein-Uhlenbeck (OU) process that yields explicit expressions for the psychometric function that describes accuracy. From these we compute strategies that optimize the rewards expected over blocks of trials administered with mixed difficulty and reward contingencies. The psychometric function is characterized by two parameters: its midpoint slope, which quantifies a subject's ability to extract signal from noise, and its shift, which measures the bias applied to account for unequal rewards. We fit these to data from two monkeys performing the moving dots task with mixed coherences and reward schedules. We find that their behaviors averaged over multiple sessions are close to optimal, with shifts erring in the direction of smaller penalties. We propose two methods for biasing the OU process to produce such shifts

Saving the world’s terrestrial megafauna

From the late Pleistocene to the Holocene, and now the so called Anthropocene, humans have been driving an ongoing series of species declines and extinctions (Dirzo et al. 2014). Large-bodied mammals are typically at a higher risk of extinction than smaller ones (Cardillo et al. 2005). However, in some circumstances terrestrial megafauna populations have been able to recover some of their lost numbers due to strong conservation and political commitment, and human cultural changes (Chapron et al. 2014). Indeed many would be in considerably worse predicaments in the absence of conservation action (Hoffmann et al. 2015). Nevertheless, most mammalian megafauna face dramatic range contractions and population declines. In fact, 59% of the world’s largest carnivores (≥ 15 kg, n = 27) and 60% of the world’s largest herbivores (≥ 100 kg, n = 74) are classified as threatened with extinction on the International Union for the Conservation of Nature (IUCN) Red List (supplemental table S1 and S2). This situation is particularly dire in sub-Saharan Africa and Southeast Asia, home to the greatest diversity of extant megafauna (figure 1). Species at risk of extinction include some of the world’s most iconic animals—such as gorillas, rhinos, and big cats (figure 2 top row)—and, unfortunately, they are vanishing just as science is discovering their essential ecological roles (Estes et al. 2011). Here, our objectives are to raise awareness of how these megafauna are imperiled (species in supplemental table S1 and S2) and to stimulate broad interest in developing specific recommendations and concerted action to conserve them

A global research priority agenda to advance public health responses to fatty liver disease

BACKGROUND & AIMS: An estimated 38% of adults worldwide have non-alcoholic fatty liver disease (NAFLD). From individual impacts to widespread public health and economic consequences, the implications of this disease are profound. This study aimed to develop an aligned, prioritised fatty liver disease research agenda for the global health community. METHODS: Nine co-chairs drafted initial research priorities, subsequently reviewed by 40 core authors and debated during a three-day in-person meeting. Following a Delphi methodology, over two rounds, a large panel (R1 n = 344, R2 n = 288) reviewed the priorities, via Qualtrics XM, indicating agreement using a four-point Likert-scale and providing written feedback. The core group revised the draft priorities between rounds. In R2, panellists also ranked the priorities within six domains: epidemiology, models of care, treatment and care, education and awareness, patient and community perspectives, and leadership and public health policy. RESULTS: The consensus-built fatty liver disease research agenda encompasses 28 priorities. The mean percentage of 'agree' responses increased from 78.3 in R1 to 81.1 in R2. Five priorities received unanimous combined agreement ('agree' + 'somewhat agree'); the remaining 23 priorities had >90% combined agreement. While all but one of the priorities exhibited at least a super-majority of agreement (>66.7% 'agree'), 13 priorities had 90% combined agreement. CONCLUSIONS: Adopting this multidisciplinary consensus-built research priorities agenda can deliver a step-change in addressing fatty liver disease, mitigating against its individual and societal harms and proactively altering its natural history through prevention, identification, treatment, and care. This agenda should catalyse the global health community's efforts to advance and accelerate responses to this widespread and fast-growing public health threat. IMPACT AND IMPLICATIONS: An estimated 38% of adults and 13% of children and adolescents worldwide have fatty liver disease, making it the most prevalent liver disease in history. Despite substantial scientific progress in the past three decades, the burden continues to grow, with an urgent need to advance understanding of how to prevent, manage, and treat the disease. Through a global consensus process, a multidisciplinary group agreed on 28 research priorities covering a broad range of themes, from disease burden, treatment, and health system responses to awareness and policy. The findings have relevance for clinical and non-clinical researchers as well as funders working on fatty liver disease and non-communicable diseases more broadly, setting out a prioritised, ranked research agenda for turning the tide on this fast-growing public health threat