Unlike a person in a wheelchair, or one who uses a cane or wears a hearing aid, some conditions - such as autism, attention deficit hyperactivity disorder (ADHD) and intellectual or developmental disabilities - are not immediately apparent.
With a greying population, Singapore has more seniors with some form of disability due to dementia and other chronic conditions. There is also an increasing number of younger people with disabilities due to strokes or accidents.
These less visible disabilities are a double-edged sword, says research fellow Justin Lee of the Institute of Policy Studies. "The more visible they are, the more it attracts stigma, but it also means help is more forthcoming.
"The less visible it is, the less likely help will be forthcoming, and it may even take some time before a person or his support network realises he has a condition," says Dr Lee.
While a person with a less visible disability may pass off as being more "normal", not talking about it leads to lower awareness and greater stigma.
Those with invisible disabilities also seem to face more prejudice, which increases with how personal the contact is.
A 2009 study in Britain found that people were more comfortable with a person with physical disabilities than learning or mental issues. And while half of the respondents were comfortable about a person with learning disabilities moving in next door or being in the same club, only 29 per cent would consider marrying them.
This mirrors an exploratory study that Mr Ho Jack Yong, assistant director of diversity and inclusion at Singapore Management University, conducted on 10 participants here.
"People seem to be more open when considering a person with disabilities as political office-holders, as co-workers," he says.
"But when we asked if people were comfortable with having a person with disability in their families as a potential romantic partner, all of a sudden there would be some discomfort."
However, Mr Ho notes that his participants, when asked about people with disabilities, immediately thought of physical disabilities and forgot that disabilities include mental and sensory impairments.
The president of the Disabled People's Association (DPA), Mr Nicholas Aw, says: "Without widening our understanding of the range of disabilities, we will never be able to adapt our society to include all persons with disabilities, and those with invisible disabilities will continue to be left behind."
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