What in the poem "Piano" brings back the memories to the poet's mind?
Probably the strongest association between the setting in which the narrator finds himself as he goes through the thoughts that are the poem and the past times that he is remembering are the types of music being experienced. In the present, as he is speaking, the narrator is in the presence of "a woman...singing to me" while accompanying herself by playing the piano.
In his memories of his childhood, the narrator is remembering another woman singing and playing a different piano. He spent many "old Sunday evenings at home" as a youngster, contentedly listening and watching from his position "under the piano" as his mother sang and played. He vividly recalls watching and probably feeling the piano strings vibrate, "pressing the small, poised feet" of his mother as she used the pedals of the piano to sustain or soften the music, and finding joy and security in listening to her sing hymns.