Invariants in the ipsilateral retinotectal visual projection of frogs.

We determined whether the sensitivity of the ipsilateral type II units of Rana esculenta to prey (W/H-oriented bars) and non-prey (A/V-oriented bars)-like targets remains invariant under various experimental conditions. We show that the shape of the 'discrimination' curve is largely unaffected by the level of general illumination and by the background texture. An increase in the stimulus velocity and in the width of the bars moderately affects the salient points (negative peak and preference reversal) of the curve, but does not alter the overall configurational preference of these units. As for retinal ganglion cells: (i) this curve expresses better a 'contrast' between two vertically oriented edges of different dimensions than a 'contrast' between two edges of equal dimension but of different orientation; and (ii) the experimentally induced variations can be explained on the basis of the spatial and temporal properties of the neuronal elements forming the antagonistic center-surround arrangement of the receptive field.

Responses of class R3 retinal ganglion cells of the frog to moving configurational bars: effect of the stimulus velocity.

Discrimination of 'prey' (bars elongated in the direction of movement; W- or H-orientation) and 'non-prey' (bars perpendicular to the direction of movement; A- or V-orientation) stimuli in freely moving amphibians is velocity-invariant. Whether or not this phenomenon is present in cells belonging to a general decision making neuronal process remains questionable. Present investigations report the effect of the angular velocity of the stimulus on the discrimination function of class R3 (transient ON-OFF) retinal ganglion cells. The main conclusions of this work are the following: (1) irrespective of the angular velocity, class R3 neurons always prefer vertically (A-) to horizontally (W-) oriented stripes as long as the stimulus length remains inferior to the receptive field size; (2) this preference for small A-stimuli is best expressed when stimuli are moved at V = 7.6 degrees/s; (3) a preference reversal is induced by stripes longer than the receptive field via a dual process involving both spatial and temporal mechanisms; (4) this preference reversal is velocity-dependent: the longer the bar, the faster the velocity should be.

Responses of ipsilateral retino-tectal (type I1) units of the frog (Rana esculenta) to moving configurational bars.

In frogs, retinal information projecting to the ipsilateral optic tectum uses a complex, at least bi-synaptic, route. Ipsilateral visual units recorded at the tectal level correspond to isthmic axon terminals. For a better approach of their visual function, these units have been stimulated with moving (V = 7.6 degrees/sec) configurational stimuli proved earlier to be able to elicit classical behavioural sequences in amphibians. In the presence of W("worm-like")-stimuli of increasing length (2 degrees < L < 20 degrees), the discharge rate of type I1 units remains rather constant. In response to A("antiworm-like")-stimuli, the discharge rate first increases up to L = 5-6 degrees and then decreases continuously. The ability of these units to discriminate bars of equal dimension but of different configuration was defined using the "contrast-like" formula originally proposed by Ewert et al. (1978). The relationship between the discrimination factor D(W, A) and the length of the stimuli is similar in shape to that found in class R3 ganglion cells. Results suggest thus that the classical functional homology between type I1 ipsilateral units and class R2 retinal neurons is inadequate.

Stimulation, data acquisition, spikes detection and time/rate analysis with a graphical programming system: an application to vision studies.

A Macintosh-based system performs stimulus control and data acquisition, and an off-line analysis, in experiments on visually driven neurons in frog. The stimulus is a target moved on a modified XY recorder. The computer is equipped with a multifunction input/output board to perform stimulus control and data acquisition. The graphical programming system LabVIEW 2 was used to develop the 'Vision 93' package made of 4 main 'virtual instruments' (VIs). By means of DOCS-Exp, the user controls the experiment via screen displays which look like front panels of electronic instruments. DOCS-Preproc performs a user-controlled spike detection and computes mean impulse rate values. DOCS-SAS displays the instantaneous frequency, mean impulse rate, spike counts or interspike time intervals as staircase histograms and/or spline smoothed curves. Finally, DOCS-x-Functions computes and graphs quantitative stimulus/response relationships in terms of velocity, diameter, orientation and configuration of the target. The functionalities of these main VIs are presented and original software components are detailed. System operation is illustrated by using the successive VIs to process a sample signal record.