The Eyes Remember It: Oculography and Pupillometry during Recollection in Three Amnesic Patients

Abstract

Two patients (TC and SS) with lesions that included the hippocampal regions (predominantly on the left side) were severely impaired in their recall of simple, verbally stated facts. However, both patients remembered spatial information that was temporally associated with semantic information. Specifically, TC and SS could not recall explicitly the content of an episode, but their spontaneous oculomotor behavior showed that they retained some information about the event as their gaze automatically returned to the locations on the computer screen where visual information had been paired to verbally presented information. Thus, this spatial information is implicit, automatically retrieved, and eye-based, as when one patient (TC) was asked to point with the finger to the same positions he was impaired. In addition, in an old/new recognition task, TC and SS and an additional patient, OB, showed significant changes in eye pupil diameter when viewing novel visual stimuli compared to stimuli that they had previously seen, also when they (incorrectly) declared with confidence that an old item was new. The spared memory of these patients, despite severe amnesia for the learning episodes, is characterized by a re-enactment of previous eye fixations that were associated with each (forgotten) episode and physiological responses (as indexed by pupillometry) to previously seen stimuli. Such spared memory can be seen as a type of "snapshot" memory, which automatically processes eye-based spatial information and whose content remains implicit. Finally, we surmise on the basis of the neuroanatomical findings of these patients, that neural substrates in the spared (right) hemisphere might support both the eye fixations' re-enactment and implicit visual pattern recognition.

Task-evoked pupillometry provides a window into the development of short-term memory capacity

“…Our STM overload task could provide insights regarding the cognitive deficits observed in specific patient populations (e.g., in amnesics, Laeng et al, 2007)—or, perhaps in the future, in individual patients. More generally, the task-evoked pupillary response could in theory be used to evaluate the effectiveness of a targeted cognitive intervention, pinpointing precisely at what stage(s) of a task the intervention influences cognitive processing.…”

Keeping an eye on the truth? Pupil size changes associated with recognition memory

“…Clearly it will be important to establish how pupil size changes in genuinely memory-impaired populations when they perform a recognition memory test. Laeng et al (2007) recently investigated the pupil old/new effect in three patients with amnesia resulting from hippocampal lesions. They found that a larger pupil response occurs for new words compared to old words in these patients.…”

Pupillary Stroop effects

“…Richardson et al 2007). Researchers can also profit from the sensitivity of pupil variations to representations and responses that are only partially activated and that may never pass the threshold for eliciting overt behavior or conscious appraisal (Bijleveld et al 2009; Laeng and Falkenberg 2007; Laeng et al 2007). Another advantage is that pupil recording can occur without any disruption of behavioral tasks.…”