Visual discrimination after anterior temporal lobectomy in humans

Objective: To determine whether right anterior temporal lobectomy (RTL) res ults in perceptual deficits, and whether the perception of particular stimu lus features (i.e., shape, motion, color) is affected differentially. Backg round: RTL results in abnormal visual discrimination, recognition, and reca ll of pictorial material that cannot be easily specified verbally, such as designs and faces. It is unclear whether stimuli must be conceptually meani ngful to elicit perceptual deficits. Methods: Tests were constructed to ass ess a wide spectrum of basic visual discrimination abilities with simple, m eaningless stimuli. The performance of nine patients who underwent left tem poral lobectomy (LTL) and nine patients who underwent RTL were compared wit h that of normal control individuals. The mean excision size along lateral cortex was 3.7 cm for the LTL group and 5.6 cm for the RTL group; mean mesi al excision size was 5.2 cm for LTL and 4.6 cm for RTL. Results: Basic visu al discrimination capacities were demonstrated to be essentially intact aft er LTL and RTL, except for a mild loss of blue color discrimination after R TL. Conclusions: There is little evidence that RTL produces perceptual impa irments limited to the domain of pattern perception, or generalizable to no nmeaningful stimuli. The perceptual loss after RTL may be largely restricte d to extraction of meaning, and related to the disruption of the circuits t hat connect the outcome of visual analysis to previously stored semantic in formation.