Methods and Materials

We measured the electrophysiological response in the retina of the diurnal rodent Octodon degus to different kinds of stimuli using a Multi Electrode Array (MEA) \citep{Litke:2004bc,Segev:2004cu} (USB MEA256, Multichannel Systems). Previous to an experiment, animals were put in darkness for \(30\min\), then deeply anesthetized with alothane and killed by beheading. Eyes were removed and dissected at room temperature under red illumination. The posterior hemisphere of the eye was cut in quadrant and the pigmented epithelium separated from the retina. Then the retina was put on a dialysis membrane (Spectra/Por Dialysis membrane 132554 MWCO: 25,000, Spectrumlabs) by the photoreceptor side and mounted on a perfusion chamber, which was then lowered onto the electrode array by the ganglion cell side. Recording was performed under perfusion with AMES medium bubbled with 95% \ceO2 5% \ceCO2 at \(33\textcelsius\). Animals were raised in captivity in a controlled facility; living conditions and experimental procedures are approved by bioethics committee of the faculty.
Stimulus presentation was performed with a conventional DLP projector using custom optics and filters to focus the image on the photoreceptor layer at a pixel size of  \(4\micro m\) at an average irradiance of \(70nW\per mm\squared\). Timing of the images was controlled using custom made software based on Psychtoolbox for MATLAB \citep{Brainard:1997we}. All data fitting procedures were performed with LMFIT \citep{newville_2014_11813}
Spike sorting was perforned using Spyking-Circus \citep{Yger:2016bi}. Data was analyzed using redistributable Jupyter notebooks running Python 3 kernels.

Characterization of spatiotemporal tuning of RGCs

To measure the sensitivity of the retina to different aspects of image stimulation, specially those related to motion, we recorded the response to gaussian white noise in a checkerboard pattern (block size = \(50\micro m\)) for \(20minutes\) at \(60Hz\) and sinusoidal drifting gratings at maximum contrast, with spatial frequencies of \numlist0.01375;0.01875;0.02625;0.0375;0.0525;0.075\(cycles\per\micro m\), and speeds of \numlist0;300;600;1200;2400;4800\(\micro m\per\sec\) in sequences of three seconds, with 10 repetitions of each sequence. Previous experiments showed that for a large part of the cell population, response to speed was independent of the direction of motion (data not shown), so the present protocol uses a single direction for all sets of stimuli.
Receptive fields were estimated from the response to the checkerboard stimulus by reverse correlation, getting the Spike-Triggered Average (STA) \citep{Chichilnisky:2001ua} as a three-dimensional spatiotemporal impulse response \FIGreport E. The spatial characterization was performed by fitting a 2 dimensional Gaussian function at the time point of maximum amplitude, then drawing an ellipse at 1 standard deviation. The size of the RF was calculated as the radius of the circle with the same area as the ellipse fit \citep{Petrusca:2007je}. The shape was quantified by the eccentricity \(\epsilon\) of the ellipse as \(\epsilon=\sqrt{1-\left(b/a\right)^{2}}\) where \(a\) and \(b\) are the major and minor radius respectively. The temporal profile was computed as the temporal course of the intensity at the point with the largest variance, and then fitted to a difference of two cascades of low-pass filters \citep{Chichilnisky:2002wu} with basal activity set to zero and normalized amplitude, that follows the form:
\begin{equation} \label{eq:temp_fit} \label{eq:temp_fit}R(t)=p_{1}\left(\frac{1}{\tau_{1}}\right)^{n}e^{-n\frac{t}{\tau_{1}-1}}-p_{2}\left(\frac{1}{\tau_{2}}\right)^{n}e^{-n\frac{t}{\tau_{2}-1}}\par \\ \end{equation}
Where \(t\) is the time in number of image frames before the spike, \(p_{1}\) and \(p_{2}\) are the amplitude responses of each filter, \(\tau_{1}\) and \(\tau_{2}\) describe the temporal decay of the response of each filter, and \(n\) is a free parameter.
Tuning to motion was evaluated from the response to the drifting gratings; the response to each set of speeds and spatial frequencies was measured by Peristimulus Time Histogram (PSTH) for 10 repetitions of each sequence, discarding the first \(200ms\) to eliminate the response to stimulus onset.
Tuning to speed \(v\) was fitted to an skewed gaussian in which the response to speed \(R(v)\) has the form
\begin{equation} \label{eq:v_fit} \label{eq:v_fit}R(v)=A\left[\exp{\left({\frac{-(\log_{2}v-\log_{2}V)^{2}}{2\times(\sigma_{v}+\zeta\times(\log_{2}v-\log_{2}V))^{2}}}\right)}-\exp{\left({\frac{-1}{\zeta^{2}}}\right)}\right]\par \\ \end{equation}
where \(V\) is the preferred speed, \(\sigma_{v}\) is the curve width, \(\zeta\) is the skew of the curve and \(A\) is a scaling factor \citep{Priebe:2006jk}. Since \(\sigma_{v}\) is highly correlated with tuning bandwidth (width of the function at half-height) \citep{Pinto:2010dt}, we used \(\sigma_{v}\) for all bandwidth related functions. Changes in tuning bandwidth were measured as the normalized difference in \(\sigma_{v}\) as
\begin{equation} \label{eq:delta_sigma} \label{eq:delta_sigma}\Delta\sigma_{v}=\frac{\sigma_{v1}-\sigma_{v2}}{\sigma_{v1}+\sigma_{v2}}\par \\ \end{equation}

Natural-like st

Electrophysiological recordings

Octodon degus were raised in captivity in a controlled facility. Experimental procedures are approved by bioethics committee and regulations from the University and in accordance with the bioethics regulation of the Chilean Research Council (CONICYT). Degus are diurnal rodents with a 30% of their photoreceptors being cones. For a complete description of the model see  \citep{Chavez:2003bn,Jacobs:2003dd}. The physiological response of RGC from the Degu was measured using different types of visual stimuli trough a Multi Electrode Array \citep{Litke:2004bc,Segev:2004cu} (USB MEA256, Multichannel Systems) and the experimental protocol follows  \citep{PalaciosMunoz:2014gi}. Briefly, prior to an experiment animals were put in darkness for \(30\min\), then deeply anesthetized with halothane and beheaded. Eyes were removed at room temperature and the cornea removed under red illumination. Thereafter the posterior hemisphere of the eye was dissected in quadrants and the pigmented epithelium separated from the retina. Finally, a piece of retina was set upon a dialysis membrane (Spectra/Por Dialysis membrane 132554 MWCO: 25,000, Spectrumlabs) and mounted on a perfusion chamber, which was then lowered onto the electrode array with the RGC side down. Recording commenced under perfusion with AMES medium bubbled with 95% O2 5% CO2 at 33ยบ and the pH adjusted to 7.4.