Behavior in a visual search task with moving dot stimuli.

Understanding the neuronal mechanisms underlying the processing of visual attention requires a well-designed behavioral task that allows investigators to clearly describe the behavioral effects of attention. Here, we introduce a behavioral paradigm in which one, two or four moving dot stimuli are used in a visual search paradigm that includes two additional attentional conditions. Two animals were trained to make a saccade to a target (a dot patch with net rightward motion) and hold central fixation if no target was present.

The functional roles of neural remapping in cortex.

Remapping is a property of some cortical and subcortical neurons that update their responses around the time of an eye movement to account for the shift of stimuli on the retina due to the saccade. Physiologically, remapping is traditionally tested by briefly presenting a single stimulus around the time of the saccade and looking at the onset of the response and the locations in space to which the neuron is responsive. Here we suggest that a better way to understand the functional role of remapping is to look at the time at which the neural signal emerges when saccades are made across a stable scene.

Learned Representation of Implied Serial Order in Posterior Parietal Cortex.

Monkeys can learn the implied ranking of pairs of images drawn from an ordered set, despite never seeing all of the images simultaneously and without explicit spatial or temporal cues. We recorded the activity of posterior parietal cortex (including lateral intraparietal area LIP) neurons while monkeys learned 7-item transitive inference (TI) lists with 2 items presented on each trial. Behavior and neuronal activity were significantly influenced by the ordinal relationship of the stimulus pairs, specifically symbolic distance (the difference in rank) and joint rank (the sum of the ranks).

Reward associations do not explain transitive inference performance in monkeys.

Most accounts of behavior in nonhuman animals assume that they make choices to maximize expected reward value. However, model-free reinforcement learning based on reward associations cannot account for choice behavior in transitive inference paradigms. We manipulated the amount of reward associated with each item of an ordered list, so that maximizing expected reward value was always in conflict with decision rules based on the implicit list order.

Transitive inference in humans (Homo sapiens) and rhesus macaques (Macaca mulatta) after massed training of the last two list items.

Transitive inference (TI) is a classic learning paradigm for which the relative contributions of experienced rewards and representation-based inference have been debated vigorously, particularly regarding the notion that animals are capable of logic and reasoning. Rhesus macaque subjects and human participants performed a TI task in which, prior to learning a 7-item list (ABCDEFG), a block of trials presented exclusively the pair FG. Contrary to the expectation of associative models, the high prior rate of reward for F did not disrupt subsequent learning of the entire list.

Implicit Value Updating Explains Transitive Inference Performance: The Betasort Model.

Transitive inference (the ability to infer that B > D given that B > C and C > D) is a widespread characteristic of serial learning, observed in dozens of species. Despite these robust behavioral effects, reinforcement learning models reliant on reward prediction error or associative strength routinely fail to perform these inferences. We propose an algorithm called betasort, inspired by cognitive processes, which performs transitive inference at low computational cost.

Functional connectivity in vergence and saccade eye movement tasks assessed using Granger Causality analysis.

Throughout the day, the human visual system acquires information using saccade and vergence eye movements. Previously, functional MRI (fMRI) experiments have shown both shared neural resources and spatial differentiation between these two systems. FMRI experiments can reveal which regions are activated within an experimental task but do not yield insight into how regions of interest (ROIs) interact with each other.

Differentiation between vergence and saccadic functional activity within the human frontal eye fields and midbrain revealed through fMRI.

Purpose: Eye movement research has traditionally studied solely saccade and/or vergence eye movements by isolating these systems within a laboratory setting. While the neural correlates of saccadic eye movements are established, few studies have quantified the functional activity of vergence eye movements using fMRI. This study mapped the neural substrates of vergence eye movements and compared them to saccades to elucidate the spatial commonality and differentiation between these systems.

Segregation of frontoparietal and cerebellar components within saccade and vergence networks using hierarchical independent component analysis of fMRI.

Purpose: Cortical and subcortical functional activity stimulated via saccade and vergence eye movements were investigated to examine the similarities and differences between networks and regions of interest (ROIs).

Methods: Blood oxygenation level-dependent (BOLD) signals from stimulus-induced functional Magnetic Resonance Imaging (MRI) experiments were analyzed studying 16 healthy subjects. Six types of oculomotor experiments were conducted using a block design to study both saccade and vergence circuits.

Vision therapy in adults with convergence insufficiency: clinical and functional magnetic resonance imaging measures.

Purpose: This research quantified clinical measurements and functional neural changes associated with vision therapy in subjects with convergence insufficiency (CI).

Methods: Convergence and divergence 4° step responses were compared between 13 control adult subjects with normal binocular vision and four CI adult subjects. All CI subjects participated in 18 h of vision therapy.

Functional anatomy of predictive vergence and saccade eye movements in humans: a functional MRI investigation.

Purpose: The purpose of this study is to investigate the functional neural anatomy that generates vergence eye movement responses from predictive versus random symmetrical vergence step stimuli in humans and compare it to a similar saccadic task via the blood oxygenation level dependent signal from functional MRI.

Methods: Eight healthy subjects participated in fMRI scans obtained from a 3T Siemens Allegra scanner. Subjects tracked random and predictable vergent steps and then tracked random and predictable saccadic steps each within a block design.