Why might visual training in one eye fail to improve performance in the other eye?

Visual training in one eye may fail to improve performance in the other eye because perceptual learning is often highly specific to the conditions of the training, including the eye used during the task.1

This lack of transfer is attributed to changes in neural processing that occur at early stages of the visual system, specifically within the primary visual cortex. Rather than being a generalized, high-level cognitive improvement, this type of learning tunes neural mechanisms to respond to input from a specific eye and a particular region of the visual field. Because these early-stage cortical neurons are often organized with specific eye dominance, training one eye does not necessarily modify the neural pathways associated with the untrained eye. Consequently, the learning remains localized to the sensory input channel that was practiced.12