1. A subject monitoring system for processing physiological information of a subject, comprising: a sensor configured to generate a physiological signal, wherein the sensor detects light attenuated by the subject; and processing equipment coupled to the sensor, wherein the processing equipment is configured to: select a first segment of the physiological signal comprising a plurality of values; select a second segment of the physiological signal comprising a plurality of values, wherein the second segment is shifted in time from the first segment; determine a correlation value between the first segment and the second segment; analyze the first segment and the second segment to determine a metric; and determine correlation information based on the correlation value and based on the metric.