<p>Placebo and nocebo effects are well-documented in pain perception and motor performance, yet their impact on cognitive performance remains unclear. Understanding these effects is relevant for designing interventions that leverage positive expectations to enhance cognitive outcomes while mitigating negative expectations, especially for older adults facing age-related cognitive decline. Furthermore, it is unclear whether these effects can be induced remotely, in the absence of direct participant-experimenter interactions. This study examined whether verbal suggestions about an intervention potential to enhance or impair cognitive performance could induce placebo and nocebo effects—both objective and subjective—in healthy older adults (aged 65–80) in an online setting. Participants completed an oddball task in auditory and visual modalities before (PRE) and after (POST) exposure to an inert acoustic intervention (i.e., the placebo/nocebo intervention). Prior to the intervention, individuals were randomly assigned to one of three groups, receiving neutral (Control), positive (Placebo), or negative (Nocebo) information about the intervention. The Nocebo group showed impaired performance at POST, consistent with the verbal suggestion, despite no negative shift in expectancy or perceived efficacy. In contrast, the Placebo group expected improvements and perceived benefits, but their performance did not differ from controls. This indicates a dissociation in objective and subjective components between placebo/nocebo effects in a perceptual and attentional task. Altogether, even without in-person interaction, nocebo effects are observable in cognitive performance in older adults. In contrast, placebo effects are limited to subjective beliefs, emphasizing the importance of additional factors such as motivation, and individual differences, in online contexts.</p>