The role of the vertical meridian in visual memory for objects.
Hornak J., Duncan J., Gaffan D.
It is widely believed that, in human and nonhuman primates, visual memories of objects are stored in the temporal lobe. Electrophysiological results in monkeys, however, indicate that when a visual scene contains two or more objects, with at least one object in each visual hemifield, neurons in the temporal lobe of each hemisphere respond only to the objects that are in the contralateral visual hemifield, and their activity is unaffected by the objects in the ipsilateral hemifield. Putting these two premises together predicts that object memory should fail, or at least suffer a substantial decrement, when an object is presented for learning and retention as part of such a scene, but crosses the vertical meridian between the learning trial and the retention test. The effect of this change should be much greater than the effect of an equal retinal translation that crosses the horizontal rather than the vertical meridian. An experiment with normal human subjects verified this prediction under conventional conditions of tachistoscopic viewing, with a single constant fixation spot. A further condition in the same experiment, however, tested the same retinal translations in a more naturalistic condition, where the retinal changes were produced by varying the position on the display screen of the fixation spot rather than of the objects. Here, there was no significant special effect of crossing the vertical meridian. We conclude that visual memories are not stored exclusively in the temporal lobe.