We examined performance in young and elderly on an implicit~lexical decision! and an explicit~recognition! memory test. The difference in lexical decision times between old and new words was equivalent in the two groups, although the elderly were slower. In both groups, recognition accuracy~lower in the elderly! was higher following semantic than nonsemantic encoding, whereas lexical decision times were unaffected. Divergent brain potentials for old and new words during lexical decisions constituted a repetition effect, which reflected greater positivity~200-800 ms! for old words, particularly over the left hemisphere; this effect was smaller and later in the elderly. An electrophysiological marker of enhanced recollection for words from the semantic encoding task took the form of a left-sided positivitỹ 500-800 ms!. The effect was smaller in the elderly than the young, providing an additional index of their impaired recognition processes.

Priming effects to words are reduced when modality changes from study to test. This change was examined here using behavioral and electrophysiological measures of priming. During the study, half of the words were presented visually and half auditorally; during a subsequent lexical decision test, all words were presented visually. Lexical decisions were faster for within- than cross-modality repetitions. In contrast, modality influenced recognition only for low-frequency words. During lexical decision, event-related brain potentials were more positive to studied than unstudied words (200-500 ms). A larger and shorter duration effect was observed for within- than cross-modality repetitions (300-400 ms). This later effect is viewed as an electrophysiological index of modality-specific processing associated with priming. Results suggest that multiple events--both modality-specific and modality-nonspecific--underlie perceptual priming phenomena.

We describe a method, based on recordings of the electroencephalogram (EEG) and eye movement potentials (electrooculogram), to track where on a screen (x,y coordinates) an individual is fixating. The method makes use of an empirically derived beam-forming filter (derived from a sequence of calibrated eye movements) to isolate eye motion from other electrophysiological and ambient electrical signals. Electrophysiological researchers may find this method a simple and inexpensive means of tracking eye movements and a useful complement to scalp recordings in studies of cognitive phenomena. The resolution is comparable to that of many commercial systems; the method can be implemented with as few as four electrodes around the eyes to complement the EEG electrodes already in use. This method may also find some specialized applications such as studying eye movements during sleep and in human-machine interfaces that make use of gaze information.