With the ideal ITI determined, I can move on to the set of core experiments: testing to see how the DCMD neuron behaves when simulated black balls of different sizes and velocities approach the grasshopper’s exposed eye. So my little friends spend about 2 hours on top of the SpikerBox for these experiments.
I continue to process the data in MatLab for better visualization. Here are the results for balls approaching from a constant initial distant of 10cm, 6cm in size, and with various velocities (-2, -4, -6, -8m/s).
Perievent histogram: showing DCMD firing frequency 2s before and 2s after the simulated collision between the eye and the object:
Raster plot: showing DCMD spiking pattern across each pair of S and v over time. DCMD firing peaks around collision for objects approaching at -2m/s, and after collision for objects approaching faster:
By Dieu My Nguyen
Now that I’ve collected ample data for the “classic” experiment of testing the DCMD response to objects approaching at various sizes and velocities, I want to keep exploring grasshopper vision. So far, the iPad screen is kept at maximum brightness, so the contrast between the white background and the black ball is high and clear. Now, can grasshoppers still see the black ball if the screen brightness is at its darkness? Let’s find out!
Grasshopper G26-072516 is the subject for this test. I performed two extreme brightness levels: the highest and lowest, each for 20 trials with 6cm balls approaching at -2m/s. Note that I measured and changed the amount of brightness by adjusting that brightness bar built into the iPad. So the “lowest” brightness is not complete, pure darkness. The black ball is still identifiable, just very low contrast with the gray background.
And… I obtained results I did not expect! At max brightness, DCMD firing rate peaks at 95Hz. At minimum brightness, it peaks at 90Hz. Very, very similar firing frequency and peaking profile.
Does this mean that grasshoppers can see in the dark?! At least I can say with these negative results that grasshoppers might be able to detect approaching objects even if they din’t highly contrast with the background.
By Dieu My Nguyen
In the ‘Preliminary data‘ log, I had begun my data collection and analysis journey. I first performed the intertrial interval, or ITI, test, to determine the ideal time between 2 stimuli so that the time is long enough to avoid the grasshoppers’ habituation to the simulated balls. The results figures I showed in that previous log showed that the 45s ITI was better than the other ITIs in giving us a nice profile of the DCMD neuron activity over time. However, of course, the data visualization could be much improved, and I have been doing that by importing the recordings (stored in JSON files by the SpikeRecorder app) into MatLab (using JSONlab). MatLab yields cleaner and to-scale figures that give us an even better idea of the DCMD profiles in different ITIs.
Here, compare! These are the old figures, not to scale and all are the same height. So I had to label them all with their frequencies:
I performed a new ITI experiment on a new grasshopper, G25-072416-01. This time, I used 3 different ITIs that I think are sufficient: 45s, 22.5s, and 1s. All other experimental parameters are kept constant: iPad screen is 0.10m from the grasshopper’s eye, balls of 0.06m radius approach at -2m/s (negative for the increasingly shortened distance between the eye and the object). 30 trials per ITI test. And the data is processed in MatLab, and it looks beautiful!
Sorry the axis labels are too small to read. Horizontal axis: time to collision, from -2 to 2 seconds. Vertical axis: Firing frequency in Hz. Firing frequency is much higher in the 45s ITI, making it a “good” ITI to use for the subsequent experiments.
By Dieu My Nguyen
