Simultaneous modeling of visual saliency and value computation improves predictions of economic choice

Many decisions we make require visually identifying and evaluating numerous alternatives quickly. These usually vary in reward, or value, and in low-level visual properties, such as saliency. Both saliency and value influence the final decision. In particular, saliency affects fixation locations and durations, which are predictive of choices. However, it is unknown how saliency propagates to the final decision. Moreover, the relative influence of saliency and value is unclear. Here we address these questions with an integrated model that combines a perceptual decision process about where and when to look with an economic decision process about what to choose. The perceptual decision process is modeled as a drift–diffusion model (DDM) process for each alternative. Using psychophysical data from a multiple-alternative, forced-choice task, in which subjects have to pick one food item from a crowded display via eye movements, we test four models where each DDM process is driven by (i) saliency or (ii) value alone or (iii) an additive or (iv) a multiplicative combination of both. We find that models including both saliency and value weighted in a one-third to two-thirds ratio (saliency-to-value) significantly outperform models based on either quantity alone. These eye fixation patterns modulate an economic decision process, also described as a DDM process driven by value. Our combined model quantitatively explains fixation patterns and choices with similar or better accuracy than previous models, suggesting that visual saliency has a smaller, but significant, influence than value and that saliency affects choices indirectly through perceptual decisions that modulate economic decisions

The Role of Visual Attention in Decision-Making: an Eye-Tracking Experiment

We use eye-tracking to examine the factors that drive consumer attention and choice at the point-of-purchase. Consumers are biased towards choosing alternatives that are visually salient because they look earlier, more often, and longer at these items than at equally, or more, liked but less salient alternatives

The Morphology of the Rat Vibrissal Array: A Model for Quantifying Spatiotemporal Patterns of Whisker-Object Contact

In all sensory modalities, the data acquired by the nervous system is shaped by the biomechanics, material properties, and the morphology of the peripheral sensory organs. The rat vibrissal (whisker) system is one of the premier models in neuroscience to study the relationship between physical embodiment of the sensor array and the neural circuits underlying perception. To date, however, the three-dimensional morphology of the vibrissal array has not been characterized. Quantifying array morphology is important because it directly constrains the mechanosensory inputs that will be generated during behavior. These inputs in turn shape all subsequent neural processing in the vibrissal-trigeminal system, from the trigeminal ganglion to primary somatosensory (“barrel”) cortex. Here we develop a set of equations for the morphology of the vibrissal array that accurately describes the location of every point on every whisker to within ±5% of the whisker length. Given only a whisker's identity (row and column location within the array), the equations establish the whisker's two-dimensional (2D) shape as well as three-dimensional (3D) position and orientation. The equations were developed via parameterization of 2D and 3D scans of six rat vibrissal arrays, and the parameters were specifically chosen to be consistent with those commonly measured in behavioral studies. The final morphological model was used to simulate the contact patterns that would be generated as a rat uses its whiskers to tactually explore objects with varying curvatures. The simulations demonstrate that altering the morphology of the array changes the relationship between the sensory signals acquired and the curvature of the object. The morphology of the vibrissal array thus directly constrains the nature of the neural computations that can be associated with extraction of a particular object feature. These results illustrate the key role that the physical embodiment of the sensor array plays in the sensing process

Evidence for Functional Groupings of Vibrissae across the Rodent Mystacial Pad.

During natural exploration, rats exhibit two particularly conspicuous vibrissal-mediated behaviors: they follow along walls, and "dab" their snouts on the ground at frequencies related to the whisking cycle. In general, the walls and ground may be located at any distance from, and at any orientation relative to, the rat's head, which raises the question of how the rat might determine the position and orientation of these surfaces. Previous studies have compellingly demonstrated that rats can accurately determine the horizontal angle at which a vibrissa first touches an object, and we therefore asked whether this parameter could provide the rat with information about the pitch, distance, and yaw of a surface relative to its head. We used a three-dimensional model of the whisker array to construct mappings between the horizontal angle of contact of each vibrissa and every possible (pitch, distance, and yaw) configuration of the head relative to a flat surface. The mappings revealed striking differences in the patterns of contact for vibrissae in different regions of the array. The exterior (A, D, E) rows provide information about the relative pitch of the surface regardless of distance. The interior (B, C) rows provide distance cues regardless of head pitch. Yaw is linearly correlated with the difference between the number of right and left whiskers touching the surface. Compared to the long reaches that whiskers can make to the side and below the rat, the reachable distance in front of the rat's nose is relatively small. We confirmed key predictions of these functional groupings in a behavioral experiment that monitored the contact patterns that the vibrissae made with a flat vertical surface. These results suggest that vibrissae in different regions of the array are not interchangeable sensors, but rather functionally grouped to acquire particular types of information about the environment

Spatiotemporal patterns of contact across the rat vibrissal array during exploratory behavior

The rat vibrissal system is an important model for the study of somatosensation, but the small size and rapid speed of the vibrissae have precluded measuring precise vibrissal-object contact sequences during behavior. We used a laser light sheet to quantify, with 1 ms resolution, the spatiotemporal structure of whisker-surface contact as five naïve rats freely explored a flat, vertical glass wall. Consistent with previous work, we show that the whisk cycle cannot be uniquely defined because different whiskers often move asynchronously, but that quasi-periodic (~8 Hz) variations in head velocity represent a distinct temporal feature on which to lock analysis. Around times of minimum head velocity, whiskers protract to make contact with the surface, and then sustain contact with the surface for extended durations (~25 – 60 ms) before detaching. This behavior results in discrete temporal windows in which large numbers of whiskers are in contact with the surface. These sustained collective contact intervals (SCCIs) were observed on 100% of whisks for all five rats. The overall spatiotemporal structure of the SCCIs can be qualitatively predicted based on information about head pose and the average whisk cycle. In contrast, precise sequences of whisker-surface contact depend on detailed head and whisker kinematics. Sequences of vibrissal contact were highly variable, equally likely to propagate in all directions across the array. Somewhat more structure was found when sequences of contacts were examined on a row-wise basis. In striking contrast to the high variability associated with contact sequences, a consistent feature of each SCCI was that the contact locations of the whiskers on the glass converged and moved more slowly on the sheet. Together, these findings lead us to propose that the rat uses a strategy of windowed sampling to extract an object’s spatial features: specifically, the rat spatially integrates quasi-static mechanical signals across whiskers during the period of sustained contact, resembling an enclosing haptic procedure

Vibrissae of the Greek column exhibit long reaches to the side.

<p>The vibrissae of column 2 (right) show convex mappings when yaw and pitch are near zero (θ = 0°, ϕ = 0°), while the vibrissae of the Greek column (left) are concave near this region. This means that the whiskers of the Greek column cannot touch the surface if the rat faces it symmetrically with a level head. The rat must either pitch its head up or down, or turn its head to the side. In all subplots black indicates a resting-contact, white indicates no contact, and the color scale indicates the value of θ_impact. To permit visual comparison across subplots, the values of θ_impact have been normalized between 0 (dark blue) and 1 (dark red).</p

Definitions of contact angles during whisking behavior.

<p><b>A.</b> θ_impact is defined as the angle between the rostral-caudal axis and the vector tangent to the base of the vibrissa when it first makes contact with the object. Note that the illustrated curvature of the whiskers reflects their intrinsic curvature and does not simulate the whisker bending against the surface. <b>B.</b> Color code for the different types of vibrissal-object contact. Vibrissae in contact with the surface before protraction begins (resting-contacts) are plotted as black circles on a schematic of the mystacial pad. Vibrissae that never contact the surface at any point during the whisk (“no-contacts”) are shown in gray. Vibrissae that make contact at a particular protraction value of the whisk are color coded according to θ_impact.</p

Behavioral data validate many predictions of the simulation.

<p><b>A.</b> Behavioral data replicate the result of <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004109#pcbi.1004109.g006" target="_blank">Fig 6B</a>. The difference in the number of contacts between the left and right arrays provides information about yaw. Each data point corresponds to one msec in the behavioral data, and the data points have been color-coded by distance for visual clarity. The black lines are fit to the behavioral data and the magenta lines correspond to the predicted slope from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004109#pcbi.1004109.g006" target="_blank">Fig 6B</a> (averaged across pitches). <b>B.</b> If a rostral vibrissa (Col 5, 6) is in contact with the surface, vibrissae of the central columns (Col 2, 3, 4) are almost guaranteed to be in contact. Similarly, if a rostral vibrissa in contact, it is rare that there is no contact by a central column vibrissa. Conversely, if a central vibrissa is in contact, the probability a rostral vibrissa being in contact is more moderate. <b>C.</b> Contact by vibrissae of the exterior rows (row A, D, E) provides information about pitch. The A row is more likely to be in contact for negative pitch values while the D and E row are more likely to be in contact for positive pitch values. The interior B and C rows show distributions intermediate between those of the A and E rows. <b>D.</b> The Greek vibrissae are able to contact the wall for large yaws and at large distances. The color of each box corresponds to the number of msec in which contact was observed for a given configuration divided by the total number of msec the rat spent in that configuration.</p