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RD01.0.0

2008 Aug 31
Summary   This is a Reichardt detector model for direction selectivity with Poisson spike generation. It consists of a set of 20 subunits aligned parallel and sequentially along the axis of preferred motion. Each subunit is an opponent mechanism that senses the visual input via a pair of point-like spatial detectors that lie in neighboring discrete spatial sampling points. The output from the left spatial detector (the one away from the preferred direction) is delayed by an ideal lowpass filter (tau = 10ms) and is then multiplied by the output from the second spatial detector, which has been highpass filtered (original signal minus an ideal lowpass filter having tua = 500ms). When tested on drifting gratings, the model has a peak SF of about 2.5 cyc/deg and peak TF of about 16 Hz.

Methods

• RD01.0.0.moo - Model parameter file.
• meth.pdf - Equations

Results

The results here were obtained using the standard single unit response file.

Tuning curves for sinusoidal gratings

• Direction - at TF 16 Hz, SF 2.5 cyc/deg
• Spatial frequency - in preferred and anti-preferred direction
• Temporal frequency - at SF 2.5 cyc/deg
• Size - at SF 2.5 cyc/deg, TF 16 Hz
• Static phase - zero spikes.

Discussion

This model has a direction tuning curve that is flat on top compared to the GaborME.0.0 model. It maintains direction selectivity for a broad range of speeds, although the TF tuning curve has two peaks, one at around 16 Hz and another below 1 Hz. The RD subunits here are similar to that described by Borst et al. (2005). If this model is modified by increaseing dx, then the it will show motion reversal for some SFs. In the current version, using dx=1 causes the Nyquist limit (set by sscale) to prevent such tuning reversal.

References

• Borst A, Flanagin VL, Sompolinsky H (2005) Adaptation without parameter change: dynamic gain control in motion detection. PNAS 102:6172--6176.