Williams argues that in the past advisors have been too focused on the financial aspects of retirement and have paid too little attention to the physical and mental realities of aging.

“It’s a bit of a blind spot,” Williams says. “We don’t take this into account as part of our natural aging process when we plan, so we’re relying on hope for the future as an investment strategy.”

Just 39 percent of investors believe they have a suitable plan for when their own mental status begins to decline, according to the study.

Many investors avoid making plans because they fear the loss of their own independence, they’re overly optimistic, they’re worried about their own mortality, and /or they tend to procrastinate making long-term plans in general.

“We’re hoping that this won’t happen to us,” Williams says. “We’re in denial that this is a real possibility, and we’re transferring that hope over to our investment behavior because we’re hoping that we don’t need assistance at all.”

That may explain why fewer than one-in-three, or 32 percent, of State Street’s respondents have discussed potential cognitive decline with their family.

In some cases, having an advisor initiate discussions on a client’s mental status may lead to planning with family members and other centers of influence, like attorneys or accountants, around the possibility.

“Combining cognitive decline with their family and finances can be overwhelming,” Williams says. “Advisors can serve as an objective sounding board and an impartial expert, there’s an opportunity for them to ensure that they are helping their clients find the right people to help guide them through the conversation, which might require bringing in a social worker, estate planning attorney or an elder care attorney.”

The first symptoms of aging-related cognitive decline appear, on average, in a client’s late 60s, but not all clients are alike, and aging isn’t the only reason an investor’s mental status may deteriorate.

State Street identified three main types of cognitive decline – Alzheimer’s Disease, the most progressive type of decline; dementia, where cognitive lapses begin to interfere with an individual’s daily life; and mild cognitive decline, or minor lapses in an individual’s short term memory. Reports from the Alzheimer’s Association estimate that 10 to 25 percent of Americans older than 65 suffer from mild cognitive decline.