Self-adjustments of variable hearing aid parameters are essential for trainable hearing aids to provide customized amplification for different listening environments. Prompted by a finding of Dreschler [Ear Hear. 29, 214-227 (2008)], this study investigates the effect of the base line (starting) response on self-adjustments of gain in different frequency bands. In a laboratory test, 24 hearing-impaired listeners adjusted the bass, treble, and overall gain to reach their preferred responses from two different base line responses for 12 different listening situations. The adjustments were repeated five times using the preferred response after each adjustment as base line response for the next adjustment. Half of the listeners further compared three different response shapes, within the range of preferred responses, pairwise ten times for preferential and perceptual discrimination. The results revealed that base line response biases were more pronounced at low frequencies and for listeners with a flat hearing loss configuration. While 83% of listeners reliably discriminated between the average selected biased responses, only 25% demonstrated reliable preferences for one response over the other. Listeners who showed preferential discrimination ability were those who were less biased by the base line response. The clinical implication is that self-adjustments should begin from an appropriately prescribed starting response.