There are a couple great images-and sounds-that increase the tension of the text. The first is the descriptions of the old man's eye, which is the catlyst for the murder: "He had the eye of a vulture—a pale blue eye, with a film over it. Whenever it fell upon me, my blood ran cold." and then later, "all a dull blue, with a hideous veil over it that chilled the very marrow in my bones." It is a great description; the reader can certainly feel the creepiness of the eye, and the accompanying horror in the blood. Then, in the first half, you have repeated descriptions of the narrator's cautious, steady, silent stalking and waiting. That alone is tense; we keep waiting for him to slip, to make a noise, to be discovered. The most effective repeated imagery (5 senses, not just sight) is that of the heartbeat, which starts off as "a low, dull, quick sound, such as a watch makes when enveloped in cotton," increases to a "hellish tattoo", and keeps getting "louder, louder!". The sound of the heartbeat increases the tension just as a movie soundtrack would, and leads to the murder and confession.
Poe uses images and imagery to help the reader feel like they are actually there, experiencing the situations and emotions, and it makes for a really great story.
With imagery being language appealing to the senses, Poe initially evokes sound imagery as his narrator, much like Roderick Usher of "The Fall of the House of Usher," declares his sensitivity to any sound: "Above all was the sense of hearing acute." This sound image suggests (foreshadows) to the reader that the narrator's overly sensitive hearing may be intrinsic to the plot and resolution and the
The narrator's self-declared lack of passion is also unnerving. He does not desire the man's gold. Instead, the reason given for the premeditated murder is the man's eye, "the eye of a vulture, a pale blue eye, with a film over it." Like the "passionless" narrator, the eye's pale blue color suggests a coldness, a coldness that creates a tension in the plot as an element of horror. Added to this cold atmosphere is the light/dark imagery created by the night and the man's room which "was as black as pitch with the thick darkness (for the shutters were close fastened, through fear of robbers)" so that the narrator must employ the lantern whose brutal laser-like beam hones in on the dreaded eye.
Another image of sound is the old man's groan. This groan of fear, horrific, is uttered by helpless man: "He was still sitting up in the bed listening [he knows]--just as I have done, night after night, hearkening to the death watches..."
In the end it is sound that unravels the narrator.