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  1. Evaluation Summary:

    This paper establishes a visually mediated gap-jumping behavioral task in freely moving mice, and shows that mice can perform the task using only monocular cues with little performance deficit, perhaps at the cost of additional active sensing movements before executing the jumping maneuver. Further, using acute optogenetic inhibition, the authors establish that the primary visual cortex is used to perform this task. Using vision to judge distance - such as the width of a gap to be crossed - is crucial for survival across taxa, and this new paradigm could be informative to those interested in using mice to study such vision-based estimation under naturalistic conditions.

    (This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 agreed to share their name with the authors.)

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  2. Reviewer #1 (Public Review):

    This manuscript uses a wide range of experimental and computational techniques to address how mice use active vision to gauge distance in a gap-jumping task. It is found that for this task, the animals can compensate for the lack of binocular vision via an increase in active head movements, to perform the overall task with similar effectiveness. When the primary visual cortex (V1) is temporarily inactivated using optogenetic techniques, the animals perform much worse, suggesting a critical role for V1 in distance estimation.

    The paper makes substantial technical advances in the understanding of gap jumping in mice. The data are convincing that the animals can rely on monocular information to nearly equal effect as binocular vision. However, the reasons for this were somewhat murky: the authors concluded that the animals performed more active sensing movement, but the use of HMMs as the only means to assess this was a weakness of the manuscript. Roughly, they showed that the "recurrent" connections in an HMM were stronger with monocular vision than binocular, i.e. the mice tended to repeat certain motifs that the authors suggest were related to sensing the distance. There are several major weaknesses with this as the only approach. First, it is unclear in plain statistical terms what differs in pre-jump behavior. Second, it is unclear how these dynamical systems motifs are related to any kind of active sensing behavior. Third, and as a consequence, it is unclear any potential mechanistic benefit of the change in pre-jump behavior.

    There are also a few weaknesses to the V1 analysis. First the only analysis of the effect of inhibiting V1 was basically that more of the animals chose not to jump. But, was their accuracy worse when they did jump? If not it is entirely unclear that V1 is involved in the distance estimation and in fact one could argue that they can judge the distance fine without V1 (which of course would not mean V1 were not used).

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  3. Reviewer #2 (Public Review):

    This is a straightforward study where the authors established a behavioral task to investigate distance estimation in mice. They show that freely moving mice can jump across a variable gap using vision. The animals' performance was not affected by monocular eyelid suture, but was impaired when visual cortex was optogenetically suppressed. They also show that mice under monocular conditions had more vertical head movements, suggesting that they were using motion parallax cues. They also used modeling to analyze behavioral state transitions and revealed subtle differences between binocular and monocular conditions. Together, this behavior and its dependence on visual cortex and independence on binocular vision could be informative to those interested in studying mouse vision under naturalistic conditions. However, the observed differences between monocular and binocular conditions (more head movements and modeling results) actually suggest that mice normally use binocular cues.

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  4. Reviewer #3 (Public Review):

    In this manuscript, the authors demonstrate mice can use monocular cues to estimate distance in a new task they developed. They developed an ethologically relevant task in freely moving mice where the animals must estimate the distance of a platform to complete a jump to be rewarded. The task can be coupled to eye tracking and optogenetics. The authors provide evidence that the eye movement compensates the head movement in maintaining gaze and the initiation of the jump depends on V1. The task is in freely moving mice and offers the possibility of genetics and/or electrophysiological interrogation of the brain circuitry in the future.

    The authors achieved their aims of demonstrating mice can use monocular cues to estimate distance, and the results are simple and convincing. Regarding the specific claims in the accuracy of mice estimating the distance and whether the monocular condition caused more head movement I have a few specific comments below.

    Most of mice behavior is systems neuroscience has been in head-fixed behavior. The electrophysiology and/or imaging equipment do not move with the animals. There has been recent advances in electrophysiological and imaging techniques that allows them to be tethered to the animals. This calls for ethologically relevant behavior in rodents. The authors demonstrated that they can combine eye tracking and optogenetic with the task. As freely moving electrophysiological recording techniques improve in the future. Researchers will be able to combine this with their task to further elucidate the circuitry underlying behavior.


    Although the paper has a simple message, most of systems neuroscience is interested in how sensory evidence, in this case, monocular cues, are encoded in the brain, and the process in which it is transformed into action. Falling short of the goal to address the circuitry underlying the behavior, we can only judge the merit of how likely the task will be adapted by the community to elucidate insights into the neural circuitry. The behavior in its current form is impossible to speculate which monocular cue the mice used to solve the task, e.g. relative size, occlusion, motion parallax etc., therefore it will be difficult to pinpoint the relevant area of interest to start the interrogation. If the interest is in motor control, the jump has many degrees of freedom and muscles involved than the classical eye movement or arm reaching tasks. It is unclear the advantages this task has. Furthermore the timing of choice and reward is poorly controlled in the trial structure of the task, so it is unclear the additional insights it can offer regarding decision making and motivation.

    An important use of mice in system neuroscience is for invasive monitoring of brain activity with electrophysiology and/or imaging. The equipment for electrophysiology and imaging often require the animals to be head fixed. This study does not attempt to expand on the behavior observed, and this will be a limitation for adaptation of the task that the authors presented.

    The authors also provide an insufficient amount of details on the task. For example, how were the platform and distance manually changed by the experimenter for each trial? This is an important manual step that limits the number trials and potentially the animals' engagement in the task. In its current form, the task will unlikely be adapted by the community. Head-free behavior and the low trial number might limit the utility of the task to systems neuroscience.

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