The spatial parameters of the stimuli were tailored to match the tuning preferences of the cell being studied and the envelope TF was typically 5.6 cyc/s. The amplitude of Y cell responses to interference patterns was found to depend smoothly on carrier TF (Figures 2A–2D; see Figure S1 available online). The carrier TF tuning curves were diverse

in shape and often broadly tuned. In a few instances, the response amplitude was almost completely invariant across the entire range of tested frequencies (Figure 2E). The majority of tuning curves (38/42) were well-described by a gamma function (average r = 0.91 ± 0.08 standard deviation http://www.selleckchem.com/screening/autophagy-signaling-compound-library.html [SD], n = 38). Tuning properties estimated from these fits are summarized in Table 1, and the distribution of peak carrier TFs is presented in Figure 2F. As a population, Y cells were found to respond well to interference patterns over a wide range of carrier TFs ranging from 0 to at least 25 cyc/s. To determine if carrier TF tuning is affected by the carrier’s direction of motion, carrier TF tuning curves were measured with the carrier drifting in opposite directions but with all other stimulus parameters GW-572016 the same (Figures 2A–2E). The two measurements

were highly correlated (average r = 0.85 ± 0.18 SD, n = 42), indicating that the carrier’s direction of motion has little effect on the shape of the carrier TF tuning curve. To quantify carrier direction selectivity, a direction tuning index (DTI) was calculated at the nonzero carrier TF that elicited the largest amplitude response (Equation 2).

Values close to zero indicate no direction selectivity and values near one indicate strong direction selectivity. The measured DTI values were low, average DTI = 0.10 ± 0.09 SD (n = 42), indicating that Y cells respond about equally well to interference patterns with carriers drifting in opposite directions. The absence of carrier direction selectivity was confirmed in measurements of carrier orientation and direction tuning at the preferred carrier TF (Supplemental Text and Figure S2). Together, the high correlations and low DTI values indicate that the carrier’s direction of motion else has little effect on Y cell carrier TF tuning. Having measured how the amplitude of Y cell responses to interference patterns depends on the carrier’s TF and direction of motion, we next wanted to determine if the responses were demodulated. To do so, we examined the temporal pattern of Y cell responses to interference patterns with the same envelope TF but different carrier TFs. The responses of a linear system and a demodulating system to interference patterns are qualitatively different. If the component frequencies of an interference pattern are within the passband of a linear system, the output of that system will oscillate predominantly at the carrier TF (if the component frequencies are outside the passband there will be no response).