1. A system configured to use semantic analysis to measure affective response at varying measuring rates, comprising: a semantic analyzer configured to receive a first segment of content comprising data representing first text; the semantic analyzer is further configured to utilize semantic analysis to generate a first feature that describes an aspect of a meaning of a portion of the first text; the semantic analyzer is further configured to generate, based on the first feature, a first indication that a first value related to a predicted emotional response to the first segment does not reach a first predetermined threshold; and a controller configured to select, based on the first indication, a first measuring rate for a device for measuring affective response of a user to the first segment; the semantic analyzer is further configured to receive a second segment of content comprising data representing second text; the semantic analyzer is further configured to utilize semantic analysis to generate a second feature that describes an aspect of a meaning of a portion of the second text; the semantic analyzer is further configured generate based on the second feature a second indication that a second value related to a predicted emotional response to the second segment does reach a second predetermined threshold; the controller is further configured to select, based on the second indication, a second measuring rate for the device for measuring affective response of the user to the second segment; wherein while operating at the first measuring rate, the device takes at least 50% fewer measurements of affective response, per unit of measurement time, compared to measurements of affective response the device takes while operating at the second measuring rate.
2. The system of claim 1 , wherein the first and second predetermined thresholds represent first and second confidence levels in predictions of emotional response, respectively; and wherein the first and second values represent confidence in predictions of emotional response to the first and second segments, respectively; whereby the first measuring rate is selected when the first indication indicates that confidence in a prediction of emotional response to the first segment does not reach the first confidence level, and the second measuring rate is selected when the second indication indicates that confidence in a prediction of emotional response to the second segment does reach the second confidence level.