Figure 1.
Response Characteristics of HSE under Various Stimulus Conditions
(A) Individual response of the right HSE to rightward (preferred-direction [PD]) and leftward (null-direction [ND]) rotation of a vertical sinusoidal grating (wavelength 20 deg, velocity 40 deg/s, contrast 0.98, azimuth ±120 deg, elevation ±50 deg).
(B) Downward view of a flight trajectory (dotted line), with head position and orientation shown every 50 ms (time colour coded: start, red; finish, green).
(C) Head yaw velocity (black) and total optic flow (green) during the flight shown in (B). Positive velocities denote leftward turns, PD for the right HSE.
(D) Membrane potential of a right HSE in response to the flight shown in (B).
(E) Average membrane potential of the right HSE as determined across trials; the entire responses including spikes were taken into account (N = 6 cells, n = 17 responses).
(F) Saccade-triggered averages, calculated from the mean responses (N = 6, one to four repetitions) of right and left HSE to two trajectories for PD (black) and ND (red) saccades (63 different saccades). Vertical line denotes time of saccade peak velocity.
(G) Same as (E), but with rotations only (position of fly fixed in centre of cage; N = 6, n = 11). Broken lines denote resting potential; red or blue vertical lines indicate peak times of PD or ND saccades, respectively. Signals in (D), (E), and (G) are shifted backwards by 22.5 ms to account for response latencies; this value was determined by cross-correlation of the yaw velocity and the corresponding response traces. Signals in (E) and (G) are low-pass filtered (with a Gaussian standard deviation of 3 ms).
Figure 2.
Properties of the Intersaccadic Stimulus for the Trajectories Used for Figure 3A
(A) Probability density function of yaw velocity (red), sideward (black), and forward (blue) velocity. Forward is parallel to the frontal axis of the fly's head; sideward is perpendicular to the head's plane of symmetry. Sideward and forward velocities were converted to angular velocities by multiplying by the nearness (equal to the inverse of the distance [16]) averaged over the trajectories and over the receptive fields of the neurons (7.02 m−1).
(B) Power spectra of yaw velocity (red), sideward (black), and forward (blue) angular velocity. Typical relative standard error of the mean (SEM) = 20%.
Figure 3.
Coherence of Stimulus Parameters with HSE Response, Intersaccadic Parts of Stimulus and Response Only
(A) Average coherence of the response of the right and left HSE (N = 5 cells) with yaw velocity (red), sideward (black), and forward (blue) velocity.
(B) Construction of control stimuli. Times i denote the start of an intersaccadic period, m is its midpoint, and s is the start of a saccade. For OT, each orientation coordinate (yaw shown) between consecutive midpoints is compressed into the saccadic period, leaving orientation constant between saccades. For OR, each position coordinate (x shown) is similarly compressed, leaving position constant between saccades.
(C) Average coherence of yaw velocity for the OR (right and left HSE, N = 2) control (red), and of sideward (black) and forward (blue) velocity for the OT (N = 3) control. Typical relative SEM = 10% for all coherences shown at (A) and (C).
Figure 4.
Coherence of Stimulus Parameters with Combined HSE Responses, Intersaccadic Parts of Stimulus and Response Only
(A) Average coherence of yaw (red), sideward (black), and forward (blue) velocity with the summed responses of right and left HSE (N = 5).
(B) Same as (A) for the subtracted responses of right and left HSE. Typical relative SEM = 10% for all coherences shown at (A) and (B).
Figure 5.
(A) Yaw velocity and average responses (n = 4, low-pass filtered with a Gaussian standard deviation of 3 ms) to behaviourally generated optic flow of a given flight trajectory in the original flight arena but also in virtual flight arenas with increasingly larger size.
(B–E) Coherence of yaw velocity (red) and sideward angular velocity (black) for different cage sizes: 40-cm edge length (original cage; B), 55 cm (C), 105 cm (D), and 235 cm (E). For (C–E) the flight was centred in the cage. Insets in (B–E): the original and the virtual arenas as seen from above.