<p>Accurate recognition of low-contrast targets in complex visual environments is essential for advanced intelligent machine vision systems. Conventional photodetectors often suffer from a weak photoresponse and a linear dependence of photocurrent on light intensity, which restricts their ability to capture low-contrast features and makes them susceptible to noise. Inspired by the adaptive mechanisms of the human visual system, we present a molybdenum disulfide (MoS₂) phototransistor with tunable sensitivity, in which the gate stack incorporates a heterostructure diode—composed of O-plasma-treated MoS₂ and pristine MoS₂—that serves as the photosensitive layer. This configuration enables light-intensity-dependent modulation of the diode’s conductance, which dynamically in turn alters the voltage distribution across the gate dielectric and transistor channel, leading to a significant photoresponse. By modulating the gate voltage, the light response range can be finely tuned, maintaining high sensitivity to low-contrast targets while suppressing noise interference. Compared to conventional photodetectors, the proposed device achieves a 1000-fold improvement in sensitivity for low-contrast signal detection and exhibits significantly enhanced noise immunity. The intelligent machine vision system built on this device demonstrates exceptional performance in detecting low-contrast targets, underscoring its promise for next-generation machine vision applications.</p>