Participants in Sperling's experiment stared at a screen on which three rows of letters were flashed for just one-twentieth of a second. If Sperling sounded a high-pitched, medium-pitched, or low-pitched tone within , the person could recall the letters in the upper, middle, or lower row.

one-third of a second

Explanation:

Participants in Sperling's experiment stared at a screen on which three rows of letters were flashed for just one-twentieth of a second. If Sperling sounded a high-pitched, medium-pitched, or low-pitched tone within one-third of a second, the person could recall the letters in the upper, middle, or lower row.

explanation:

with the profits from the european sales, merchants purchased europe's manufactured  goods, including tools and weapons. then the merchants shipped those manufactured  goods, along with the  american  sugar and rum, to west africa where they were bartered for  slaves.

to stay where they were until m sent for