Object comparison in the lateral intraparietal area

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. Based on data obtained using this approach, we suggest that remapping in the lateral intraparietal area is sufficient to play a role in maintaining visual stability across saccades, whereas in the frontal eye field, remapped activity carries information that affects future saccadic choices and, in a separate subset of neurons, is used to maintain a map of locations in the scene that have been previously fixated.

The roles of the lateral intraparietal area and frontal eye field in guiding eye movements in free viewing search behavior

The lateral intraparietal area (LIP) and frontal eye field (FEF) have been shown to play significant roles in oculomotor control, yet most studies have found that the two areas behave similarly. To identify the unique roles each area plays in guiding eye movements, we recorded 200 LIP neurons and 231 FEF neurons from four animals performing a free viewing visual foraging task. We analyzed how neuronal responses were modulated by stimulus identity and the animals' choice of where to make a saccade. We additionally analyzed the comodulation of the sensory signals and the choice signal to identify how the sensory signals drove the choice. We found a clearly defined division of labor: LIP provided a stable map integrating task rules and stimulus identity, whereas FEF responses were dynamic, representing more complex information and, just before the saccade, were integrated with task rules and stimulus identity to decide where to move the eye.NEW & NOTEWORTHY The lateral intrapareital area (LIP) and frontal eye field (FEF) are known to contribute to guiding eye movements, but little is known about the unique roles that each area plays. Using a free viewing visual search task, we found that LIP provides a stable map of the visual world, integrating task rules and stimulus identity. FEF activity is consistently modulated by more complex information but, just before the saccade, integrates all the information to make the final decision about where to move.

Synchronization between frontal eye field and area V4 during free-gaze visual search

Information flow between the prefrontal and visual cortices is critical for visual behaviors such as visual search. To investigate its mechanisms, we simultaneously recorded spike and local field potential (LFP) signals in the frontal eye field (FEF) and area V4 while monkeys performed a free-gaze visual search task. During free-gaze search, spike-LFP coherence between FEF and V4 was enhanced in the theta rhythm (4-8 Hz) but suppressed in the alpha rhythm (8-13 Hz). Cross-frequency couplings during the Cue period before the search phase were related to monkey performance, with higher FEF theta-V4 gamma coupling and lower FEF alpha-V4 gamma coupling associated with faster search. Finally, feature-based attention during search enhanced spike-LFP coherence between FEF and V4 in the gamma and beta rhythms, whereas overt spatial attention reduced coherence at frequencies up to 30 Hz. These results suggest that oscillatory coupling may play an important role in mediating interactions between the prefrontal and visual cortices during visual search.

Parietal-Occipital Interactions Underlying Control- and Representation-Related Processes in Working Memory for Nonspatial Visual Features

Although the manipulation of load is popular in visual working memory research, many studies confound general attentional demands with context binding by drawing memoranda from the same stimulus category. In this fMRI study of human observers (both sexes), we created high- versus low-binding conditions, while holding load constant, by comparing trials requiring memory for the direction of motion of one random dot kinematogram (RDK; 1M trials) versus for three RDKs (3M), or versus one RDK and two color patches (1M2C). Memory precision was highest for 1M trials and comparable for 3M and 1M2C trials. And although delay-period activity in occipital cortex did not differ between the three conditions, returning to baseline for all three, multivariate pattern analysis decoding of a remembered RDK from occipital cortex was also highest for 1M trials and comparable for 3M and 1M2C trials. Delay-period activity in intraparietal sulcus (IPS), although elevated for all three conditions, displayed more sensitivity to demands on context binding than to load per se. The 1M-to-3M increase in IPS signal predicted the 1M-to-3M declines in both behavioral and neural estimates of working memory precision. These effects strengthened along a caudal-to-rostral gradient, from IPS0 to IPS5. Context binding-independent load sensitivity was observed when analyses were lateralized and extended into PFC, with trend-level effects evident in left IPS and strong effects in left lateral PFC. These findings illustrate how visual working memory capacity limitations arise from multiple factors that each recruit dissociable brain systems.SIGNIFICANCE STATEMENT Visual working memory capacity predicts performance on a wide array of cognitive and real-world outcomes. At least two theoretically distinct factors are proposed to influence visual working memory capacity limitations: an amodal attentional resource that must be shared across remembered items; and the demands on context binding. We unconfounded these two factors by varying load with items drawn from the same stimulus category ("high demands on context binding") versus items drawn from different stimulus categories ("low demands on context binding"). The results provide evidence for the dissociability, and the neural bases, of these two theorized factors, and they specify that the functions of intraparietal sulcus may relate more strongly to the control of representations than to the general allocation of attention.