Anyone familiar with parrotlets know that they thrive in a stimulating environment, but just how much stimulation is good without being too much...
I view my parrotlets like toddlers. Although these little dynamos crave mental stimulation, at some point, these guys can crash and burn with too much of a good thing. Research concludes that birds are happiest when provided with a variety of enrichment. These various forms of enrichment can include toys, visual and auditory stimuli, and human interaction. Factors additional to these three basic items can be the location/embellishment of the cage, lighting of the cage and room, and foraging opportunities.
About the cage, we know that a change of scenery is often a refreshing point of view for a person, so it stands to reason that it could also be refreshing for your p'let. One thing that can be done is to simply change the location of your cage within the room. Providing a different location reveals a new vantage point from your parrotlet's view. Sort of like rearranging your furniture to give a room a fresh look, relocating your cage can give your parrotlet a completely different, and refreshing, view of their surroundings. Another thing that I like to do is to change out the foliage surrounding my cages. I often find silk palms or other silk plants at my local thrift stores. Once washed, these plants can turn you bird's cage into a simulated forest. Since I have lights above my cages, silk foliage allow my pets to dart in and out of the light, just as they would under a forest canopy. (see below for the tops of two of my aviary cages for examples)
Creating foraging opportunities for your parrotlet is another simple yet stimulating option. I often wrap millet or other small treats, like sunflower seeds, in brown paper. My birds love tearing through this paper to reveal their prize. Additionally, I like to place air popped popcorn on top of their cages. They can perform all sorts of entertaining maneuvers and contortions getting to this treat.
Lighting can be another environmental factor that can bring not only a room, but your parrotlet, to life. We all understand how sunlight improves mood and energy in humans. Birds can benefit from the same application of both natural and artificial lighting. Since birds do benefit from natural sunlight, allowing them access to sunning themselves, even for a brief period of time, can be beneficial. Even if you don't have a screened in porch, or do not feel comfortable with taking your parrotlet outside in a small cage, placing a perch on a windowsill can provide the much desired light and warmth for your bird to enjoy.