No, low, full, and high speeds all use differential signaling. Differential zero is when D+ is logic low and D- is logic high as defined by the USB 2.0 spec. Differential one is when D+ is logic high and D- is logic low as defined by the USB 2.0 spec. Data travels in one direction at a time.
See 7.1.7 in the USB 2.0 spec.