Editing Bottom-up and top-down design (section)

== Natural sciences ==

=== Nanotechnology ===
{{Main article|Nanotechnology}}
[[File:Nanoparticle synthesis techniques.jpg|thumb|right|Nanoparticle synthesis techniques]]

Top-down and bottom-up are two approaches for the manufacture of products. These terms were first applied to the field of nanotechnology by the [[Foresight Institute]] in 1989 to distinguish between molecular manufacturing (to mass-produce large atomically precise objects) and conventional manufacturing (which can mass-produce large objects that are not atomically precise). Bottom-up approaches seek to have smaller (usually [[Molecule|molecular]]) components built up into more complex assemblies, while top-down approaches seek to create nanoscale devices by using larger, externally controlled ones to direct their assembly. Certain valuable nanostructures, such as [[Silicon nanowire#Synthesis|Silicon nanowires]], can be fabricated using either approach, with processing methods selected on the basis of targeted applications.

A top-down approach often uses the traditional workshop or microfabrication methods where externally controlled tools are used to cut, mill, and shape materials into the desired shape and order. [[Micropatterning]] techniques, such as [[photolithography]] and [[inkjet printing]] belong to this category. Vapor treatment can be regarded as a new top-down secondary approaches to engineer nanostructures.<ref>{{cite journal|last1=Saghaei|first1=Jaber|last2=Fallahzadeh|first2=Ali|last3=Saghaei|first3=Tayebeh|title=Vapor treatment as a new method for photocurrent enhancement of UV photodetectors based on ZnO nanorods|journal=Sensors and Actuators A: Physical|date=June 2016|volume=247|pages=150–155|doi=10.1016/j.sna.2016.05.050|bibcode=2016SeAcA.247..150S }}</ref>

Bottom-up approaches, in contrast, use the chemical properties of single molecules to cause single-molecule components to (a) self-organize or self-assemble into some useful conformation, or (b) rely on positional assembly. These approaches use the concepts of [[molecular self-assembly]] and/or [[molecular recognition]]. See also [[Supramolecular chemistry]]. Such bottom-up approaches should, broadly speaking, be able to produce devices in parallel and much cheaper than top-down methods but could potentially be overwhelmed as the size and complexity of the desired assembly increases.

=== Neuroscience and psychology ===
[[Image:TheCat.png|thumb|right|An example of top-down processing: Even though the second letter in each word is ambiguous, top-down processing allows for easy disambiguation based on the context.]]

These terms are also employed in [[Cognitive science|cognitive sciences]] including [[neuroscience]], [[cognitive neuroscience]] and [[cognitive psychology]] to discuss the flow of information in processing.{{sfn|Palmer|Rosch|Chase|1981|p=}}{{page needed |date=March 2017}} Typically, [[Sensory system|sensory]] input is considered bottom-up, and [[Executive functions|higher cognitive processes]], which have more information from other sources, are considered top-down. A bottom-up process is characterized by an absence of higher-level direction in sensory processing, whereas a top-down process is characterized by a high level of direction of sensory processing by more cognition, such as goals or targets (Biederman, 19).<ref name="autogenerated1"/>{{failed verification|date=November 2024}}

According to college teaching notes written by Charles Ramskov,{{who|date=March 2017}} Irvin Rock, Neiser, and Richard Gregory claim that the top-down approach involves perception that is an active and constructive process.{{sfn|Ramskov|2008|p=67}}{{better source needed|date=March 2017}} Additionally, it is an approach not directly given by stimulus input, but is the result of stimulus, internal hypotheses, and expectation interactions. According to theoretical synthesis, "when a stimulus is presented short and clarity is uncertain that gives a vague stimulus, perception becomes a top-down approach."<ref name="autogenerated1935">{{cite web |url=http://psychclassics.asu.edu/Stroop/ |title=Classics in the History of Psychology – Stroop (1935) |publisher=Psychclassics.asu.edu |date=August 15, 1934 |access-date=October 21, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20140119172853/http://psychclassics.asu.edu/Stroop/ |archive-date=January 19, 2014 |df=mdy-all }}</ref>

Conversely, psychology defines bottom-up processing as an approach in which there is a progression from the individual elements to the whole. According to Ramskov, one proponent of bottom-up approach, Gibson, claims that it is a process that includes visual perception that needs information available from proximal stimulus produced by the distal stimulus.{{sfn|Ramskov|2008|p=}}{{page needed|date=March 2017}}{{better source needed|date=March 2017}}{{sfn|Solso|1998|p=15}} Theoretical synthesis also claims that bottom-up processing occurs "when a stimulus is presented long and clearly enough."<ref name="autogenerated1935"/>

Certain cognitive processes, such as fast reactions or quick visual identification, are considered bottom-up processes because they rely primarily on sensory information, whereas processes such as [[motor system|motor]] control and [[Overt attention|directed attention]] are considered top-down because they are goal directed. Neurologically speaking, some areas of the brain, such as area [[Visual cortex#Primary visual cortex (V1)|V1]] mostly have bottom-up connections.<ref name="autogenerated1935"/> Other areas, such as the [[fusiform gyrus]] have inputs from higher brain areas and are considered to have top-down influence.{{sfn|Ramskov|2008|p=81}}{{better source needed|date=March 2017}}

The study of [[Attention|visual attention]] is an example. If your attention is drawn to a flower in a field, it may be because the color or shape of the flower are visually salient. The information that caused you to attend to the flower came to you in a bottom-up fashion—your attention was not contingent on knowledge of the flower: the outside stimulus was sufficient on its own. Contrast this situation with one in which you are looking for a flower. You have a representation of what you are looking for. When you see the object, you are looking for, it is salient. This is an example of the use of top-down information.

In cognition, two thinking approaches are distinguished. "Top-down" (or "big chunk") is stereotypically the visionary, or the person who sees the larger picture and overview. Such people focus on the big picture and from that derive the details to support it. "Bottom-up" (or "small chunk") cognition is akin to focusing on the detail primarily, rather than the landscape. The expression "seeing the wood for the trees" references the two styles of cognition.<ref>{{cite journal | last1 = Biederman | first1 = I. | last2 = Glass | first2 = A. L. | last3 = Stacy | first3 = E. W. | year = 1973 | title = Searching for objects in real world scenes | journal = Journal of Experimental Psychology | volume = 97 | issue = 1| pages = 22–27 | doi=10.1037/h0033776| pmid = 4704195 }}</ref>

Studies in task switching and response selection show that there are differences through the two types of processing. Top-down processing primarily focuses on the attention side, such as task repetition.{{sfn|Schneider|2015}}{{page needed |date=May 2025}} Bottom-up processing focuses on item-based learning, such as finding the same object over and over again.{{sfn|Schneider|2015}} 
{{page needed |date=May 2025}} Implications for understanding attentional control of response selection in conflict situations {{incomprehensible span |date=May 2025 |reason=Are discussed where, by whom? In Schneider? |text=are discussed.}}{{sfn|Schneider|2015}}{{page needed |date=May 2025}}

This also applies to how we{{who|date=December 2023}} structure these processing neurologically. With structuring information interfaces in our neurological processes for procedural learning. These processes were proven effective to work in our{{who|date=December 2023}} interface design. But although both top-down principles were effective in guiding interface design; they were not sufficient. They can be combined with iterative bottom-up methods to produce usable interfaces .<ref>{{harvnb|Zacks|Tversky|2003}}</ref>{{clarify|date=January 2023}}

Undergraduate (or bachelor) students are taught the basis of top-down bottom-up processing around their third year in the program.{{citation needed|date=December 2023}} Going through four main parts of the processing when viewing it from a learning perspective. The two main definitions are that bottom-up processing is determined directly by environmental stimuli rather than the individual's knowledge and expectations.{{sfn|Koch|2022}}

===Public health===

Both top-down and bottom-up approaches are used in public health. There are many examples of top-down programs, often run by governments or large [[inter-governmental organizations]]; many of these are disease-or issue-specific, such as [[HIV]] control or [[smallpox]] [[Eradication of infectious diseases|eradication]]. Examples of bottom-up programs include many small NGOs set up to improve local access to healthcare. But many programs seek to combine both approaches; for instance, [[guinea worm eradication]], a single-disease international program currently run by the [[Carter Center]] has involved the training of many local volunteers, boosting bottom-up capacity, as have international programs for hygiene, sanitation, and access to primary healthcare.

=== Ecology ===
[[File:Limiting factors in ecology figure.svg|thumb|right|The [[energy pyramid]] represents the ecosystem and its layers, the symbols represent the various limiting factors.]]

In [[ecology]] top-down control refers to when a top predator controls the structure or population dynamics of the [[ecosystem]]. The interactions between these top predators and their prey are what influences lower [[trophic level]]s. Changes in the top level of trophic levels have an inverse effect on the lower trophic levels. Top-down control can have negative effects on the surrounding ecosystem if there is a drastic change in the number of predators. The classic example is of [[kelp forest]] ecosystems. In such ecosystems, [[sea otter]]s are a [[keystone species|keystone]] predator. They prey on [[Sea urchin|urchins]], which in turn eat kelp. When otters are removed, urchin populations grow and reduce the kelp forest creating [[urchin barren]]s. This reduces the diversity of the ecosystem as a whole and can have detrimental effects on all of the other organisms. In other words, such ecosystems are not controlled by productivity of the kelp, but rather, a top predator. One can see the inverse effect that top-down control has in this example; when the population of otters decreased, the population of the urchins increased.

Bottom-up control in ecosystems refers to ecosystems in which the nutrient supply, productivity, and type of [[primary producer]]s (plants and phytoplankton) control the ecosystem structure. If there are not enough resources or producers in the ecosystem, there is not enough energy left for the rest of the animals in the food chain because of [[biomagnification]] and [[ecological efficiency]]. An example would be how plankton populations are controlled by the availability of nutrients. Plankton populations tend to be higher and more complex in areas where [[upwelling]] brings nutrients to the surface.

There are many different examples of these concepts. It is common for populations to be influenced by both types of control, and there are still debates going on as to which type of control affects food webs in certain ecosystems.