Answer:
Ceiling
Step-by-step explanation:
Ceiling effect is a research term, that describes the a situation in which subjects or participants scores stays at the upper end of the measurement.
It is also used in describing a phenomenon, in which independent variable (in this case, noise level) no longer has an effect on a dependent variable (participants) after some form of saturations has been reached.
Hence, in this case, the researcher finds that the participants who were tested received the highest scores for their comprehension irrespective of the noise levels, which is most likely due to a CEILING effect.