Recent physiological studies in animals have shown that noise-induced “temporary threshold shift” can result in a large and permanent loss of synaptic connections between the inner hair cells and the auditory nerve, without any measurable change in absolute thresholds. As audiometric absolute thresholds are the current clinical standard for diagnosing human hearing loss, this form of synaptopathy may remain undiagnosed, or hidden, with its perceptual consequences remaining unclear. Baseline expectations for perceptual consequences can be derived from a simple application of the principles of signal detection theory using a set of simplifying assumptions, such as independent and equal information from each auditory nerve fiber, and optimal integration of information. This approach shows that quite dramatic losses (e.g., 50%) lead to relatively small changes in predicted behavioral thresholds (1.5 dB in this case), which may not be easily detectable. However, synaptopathy that selectively affects specific neural populations, such as low-spontaneous-rate fibers, may result in larger and more measurable perceptual effects. Preliminary data from our lab also suggest that physiological measures, such as changes in wideband acoustic reflectance via the middle-ear muscle reflex, may provide a sensitive measure of synaptopathy in humans. [Work supported by NIH grant R01DC005216.]