Visual attention fluctuates over time and modulates information processing periodically: theta frequency (4-7 Hz) during spatial exploration, and alpha frequency (8-12 Hz) when attention is sustained at a given location. We hypothesized that such rhythms in behavioral performance accompany fluctuations in the quality of sensory representations, and specifically, (1) changes in the tuning to relevant features, and/or (2) enhancement (gain) of the target stimulus feature, and/or (3) suppression of irrelevant features. We tested this hypothesis using a psychophysics reverse correlation paradigm in which participants were instructed to deploy endogenous (voluntary) attention across two possible spatial locations (bottom left or right quadrant). Participants were asked to discriminate the gap position of a cued (valid; 2/3) or uncued (invalid, necessitating attentional reorienting; 1/3) Landolt-C. In the same trial, after a variable delay, two noise patches were presented at the same two locations, and participants had to detect the presence of a Gabor in each patch independently (50% present). The first discrimination task was used to manipulate attention while the subsequent detection task probed attention at each location and delay. Our results replicated the rhythmic fluctuations of sensitivity (d’) found in previous experiments. For sustained attention, d’ fluctuated at the alpha frequency, and when attention was reoriented (exploration) d’ fluctuated at the theta frequency. Critically, the results of the reverse correlation analysis suggest that the representations of irrelevant features were rhythmically suppressed during sustained attention, and the relevant target feature was rhythmically enhanced during exploratory attention.